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HISTOLOGY 


By  the  same  Juthor. 

DIRECTIONS    FOR    CLASS    WORK 
IN    PRACTICAL    PHYSIOLOGY: 

Elementary  Physiology  of  Muscle  and  Nerve  and 
of  the  Vascular  and  Nervous  Systems. 

With  48  Diagrams  to  shcnu  arrangement  of  Apparatus. 
8vo.     3s.   net. 

LONDON  :    LONGMANS.  GREEN  &  CO. 


A   COURSE   OF   PRACTICAL    HISTOLOGY 

Containing  plain  directions  for  individual 

work  in  Histology. 

8vo.     7s.  6d. 

LONDON :    SMITH,  ELDER  &  CO. 


THE    essentials''"'*'^ 


OF 


IT  1  S  T  O  L  O  G  Y 


DESCRIPTIVE  AND  PRACTICAL 


FOE  THE  USE  OF  STUDE.YTS 


BY 


E.  A.  SCHAFER,  LL.IX,  8c.D.,  F.K.t^. 

PROFESSOR    OF    PHTSIOLOGY    IN    THE    UNIVERSITY    OF    EDINBURGH 
FORMERLY  .lODRELL  PROFESSOR   OF  PHYSIOLOGY   IN  UNIVERSITY  COLLEGE,    LONDON 


SEVENTH  EDITION 


LEA  BROTHERS  &  CO. 

PHILADELPHIA    AND     NEW     YORK 
1907 


Ho7 


PREFACE  TO  THE  SEVENTH  EDITION. 


This  Book  is  written  with  the  object  of  supplying  the  student  with 
directions  for  the  microscopical  examination  of  the  tissues.  At  the 
same  time  it  is  intended  to  serve  as  an  Elementary  Text-book  of 
Histology ;  comprising  the  essential  facts  of  the  science,  liut 
omitting  less  important  details. 

For  conveniently  accompanying  the  work  of  a  class  of  medical 
students,  the  book  is  divided  into  fifty  lessons.  Each  of  these 
may  be  supposed  to  occupy  from  one  to  three  hours,  according  to 
the  relative  extent  to  which  the  preparations  are  made  beforehand 
by  the  teacher,  or  during  the  lesson  by  the  students.  A  few  of 
the  preparations  cannot  well  be  made  by  a  class,  but  it  has  been 
thought  advisable  not  to  injure  the  completeness  of  the  work  by 
omitting  mention  of  them. 

Only  those  methods  are  recommended  upon  which  experience  has 
proved  that  full  dependence  can  be  placed,  but  the  directions  given 
are  for  the  most  part  capable  of  easy  verbal  modification  in  accord- 
ance with  the  ideas  or  experience  of  different  teachers. 

The  present  edition  has  been  considerably  enlarged,  partly  by 
additions   to   the   text — especially  that   descriptive  of   the   structure 


vi  PKEFACE. 

of  the  central  nervous  system,  a  proper  knowledge  of  which  is 
essential  to  students  of  medicine — partly  by  the  provision  of  new 
illustrations  derived  from  many  sources.  The  author  desires  to 
express  his  recognition  of  the  readiness  with  which  other  authors 
have  placed  illustrations  at  his  disposal.  This  recognition  is 
especially  due  to  Professor  Sobotta  and  to  Professor  Ram6n  Cajal, 
the  latter  of  whom  was  good  enough  to  lend  many  of  his  original 
drawings  for  reproduction  in  this  work. 

A  new  feature  is  the  printing  of  many  of  the  illustrations  in 
colour,  which  it  is  believed  will  give  a  better  idea  of  the  appear- 
ance of  the  stained  preparations. 

To  Dr.  P.  T.  Herring,  who  has  read  and  corrected  the  final 
proofs ;  and  to  Professor  Sherrington,  who  has  looked  through  the 
chapters  on  the  central  nervous  system,  the  author  begs  to  offer 
his  grateful  acknowledgments. 


CONTENTS. 


INTRODUCTORY. 

PAGE 

Enumeration  of  the  Tissues — General  Structure  of  Animal  Cells,        1 


LESSON   I. 
Use  of  the  Microscope — Examination  of  Common  Objects,      .        .         24 

LESSONS  II.  and  III. 

Human   Blood-Corpuscles — Development   of   Blood-Corpuscles — 

Bone-Marrow,        .        .     ' 28 

LESSON   IV. 
Action  of  Reagents  upon  the  Human  Blood-Corpuscles,  .        .         41 

LESSON   V. 
Blood-Corpuscles  of  Amphibia, 45 

LESSON   VI. 
Amceboid  Phenomena  of  the  Colourless  Blood-Corpuscles,         .        48 

LESSON   VII. 
Epithelium, 52 


viii  CONTENTS. 

LESSON   VIII. 

PAGE 

Columnar  and  Ciliated  Epithelium, 60 


LESSON   IX. 

Connective    Tissues  :    Areolar    and    Adipose   Tissue — Retiform 

Tissue, 67 

LESSON   X. 

Connective  Tissues  {continued)  :  Elastic  Tissue — Fibrous  Tissue- 
Development  OF  Connective  Tissue,   ......        78 


LESSON   XI. 

Connective  Tissues  {continued) :   Articular   Cartilage — Synovial 

Membranes, 86 


LESSON  XII. 

Connective     Tissues      {continued) :       Costal     Cartilage— Fibro- 

Cartil.\ge,       ...........         92 


LESSON   XIII. 

Connective    Tissues    {continued)  :     Structure    and    Development 

of  Bone, 96 


LESSON   XIV. 
Striated  Muscle, 110 

LESSON   XV. 

Connection  of  Muscle  with  Tendon — Blood- Vessels  of  Muscle — 

Cardiac  Muscle — Development  of  Muscle — Plain  Muscle,         120 

LESSON   XVI. 
Nerve-Fibres, "     128 


CONTENTS.  ix 

LESSONS  XVII.  AND  XVIII. 

PAGE 

Nerve-Cells — Neuroglia — Development     of     Nerve-Fibres    and 

Nerve-Cells — Degeneration  and  Regeneration,      .         .         .137 

LESSON  XIX. 
Modes  of  Termination  of  Nerve-Fibres, 166 

LESSON    XX. 
The  Larger  Blood-Vessels, 184 

LESSON   XXI. 

Smaller  Blood-Vessels — Ltmph-Vessels — Serous  Membranes. — 
Microscopic  Study  of  the  Circulation — Development  of 
Blood-  and  Ltmph-Vessels, 191 

LESSON   XXII. 
Lymph-Glands — Tonsil— Thymus, 203 

LESSON   XXIII. 
Spleen — Suprarenal  Capsules — Thyroid  Body — Pituitary  Body,       213 

LESSONS  XXIV.  and  XXV. 

Skin,  Nails,  Hairs,  etc. — Mammary  Glands, 226 

LESSON   XXVI. 
Heart, 250 

LESSON   XXVII. 
Trachea  and  Lungs, 254 


X  CONTENTS. 

LESSON   XXVIII. 

PAGE 

Structure  and  Development  of  the  Teeth,    .        .        .         .        .       263 


LESSON   XXIX. 

Tongue   and   Mucous  Membrane    of    the   Mouth — Taste-Buds — 

Pharynx  and  Oesophagus, 275 


LESSON  XXX. 
Salivary  Glands, 281 

LESSON   XXXI. 
Stomach, 287 

LESSONS  XXXII.  AND  XXXIII. 

Small  and  Large  Intestine, :        .       295 

LESSONS  XXXIV.  and  XXXV. 

Liver  and  Pancreas, 309 

LESSON   XXXVI. 
Kidney, 320 

LESSON   XXXVII. 

Ureter,  Bladder,  and  Male  Generative  Organs,    .    .    .   328 

LESSON   XXXVIII. 

Generative  Organs  of  the  Female, 344 

LESSON  XXXIX.  AND  XL. 
Spinal  Cord, 355 


CONTENTS.  xi 

LESSON   XLI. 

PAOK 

Medulla  Oblongata, 374 


LESSONS  XLII.  AND  XLIIL 
Pons  Varolii,  Mesencephalon,  and  Thalamencephalon,        .         .       390 

LESSONS  XLIV.  and  XLV. 
Cerebellum  and  Cerebrum, 417 

LESSONS  XLYI.,  XLVII.  and  XLVIII. 
Eye, 443 

LESSON   XLIX. 
Olfactory  Mucous  Membrane— External  and  Middle  Ear,        .       467 

LESSON   L. 
Internal  Ear, 472 

APPENDIX. 
Methods, 484 

INDEX, 501 


THE  ESSENTIALS   OF  HISTOLOGY 


INTRODUCTORY. 

EX  U  ME  RATION  OF  THE   TISSUES  AND   THE  GENERAL 
STRUCTURE  OF  ANIMAL   CELLS. 

Animal  Histology ^  is  the  science  which  treats  of  the  minute  struc- 
ture of  the  tissues  and  organs  of  the  animal  body  ;  it  is  studied  with 
the  aid  of  the  microscope,  and  is  therefore  also  termed  Microscopic 
Anatomy. 

Every  part  or  organ  of  the  body,  when  separated  into  minute 
fragments,  or  when  examined  in  thin  sections,  is  found  to  consist 
of  certain  textures  or  tissues,  which  differ  in  their  arrangement  in 
different  organs,  but  each  of  which  exhibits  characteristic  structural 
features. 

The  following  is  a  list  of  the  principal  tissues  which  compose  the 
body  :— 

1.  Epithelial. 

2.  Connective :  Areolar,  Fibrous,  Elastic,  Adipose,  Lymphoid, 
Cartilage,  Bone. 

3.  Muscular :  Voluntary,  Involuntary  or  plain.  Cardiac. 

4.  Nervous. 

Some  organs  are  formed  of  several  of  the  above  tissues,  others 
contain  only  one  or  two. 

It  is  convenient  to  include  such  fluids  as  the  hlood  and  lymph 
amongst  the  tissues,  because  they  are  studied  in  the  same  manner 
and  contain  cellular  elements  similar  to  those  met  with  in  some  of 
the  other  tissues. 

All  the  tissues  are,  prior  to  differentiation,  masses  of  cells  (embryonic 
cells).  In  some  tissues  other  tissue-elements  become  developed 
which  take  the  form  of  fibres.  Thus  the  epithelial  tissues  are  com- 
posed   throughout   life    entirely   of    cells,    only    slightly   modified    in 

^  From  tffToy,  a  web  or  texture. 
A 


THE   ESSENTIALS   OF   HISTOLOGY, 


structure,  and  the  nervous  and  muscular  tissues  are  formed  of  cells 
which  are  greatly  modified  to  form  the  characteristic  fibres  of  those 
tissues.  On  the  other  hand,  in  the  connective  tissues  an  amorphous 
material  becomes  formed  between  the  cells  which  is  termed  intercellular 
substance  or  ground  substance,  and  in  this  substance  fibres  make  their 
appearance,  sometimes,  as  in  the  fibrous  connective  tissue,  in  so  large 
an  amount  as  to  occup}'  the  whole  of  the  intercellular  substance,  and 
greatly  to  preponderate  over  the  cells.  This  ground  substance,  by 
virtue  of  its  containing  a  certain  amount  of  inorganic  chlorides,  has 
the  property  of  becoming  stained  brown  or  black  by  nitrate  of 
silver  and  subsequent  exposure  to  light,  in  which  case  the  cells, 
which  remain  unstained,  look  like  white  spaces  (cell-spaces)  in  the 
ground  substance.  When  an  epithelial  tissue  is  similarly  treated,  the 
narrow  interstices  between  the  cells  are  also  stained,  from  which  it  may 
be  concluded  that  a  similar  substance  exists  in  small  amount  between 
the  cells  of  this  tissue.  It  has  here  been  termed  cement-substance,  but 
it  is  better  to  apply  to  it  the  general  term  intercellular  substance. 

The  cells  of  a  tissue  are  not  always  separate  from  one  another,  but 
are  in  many  cases  connected  by  bridges  of  the  cell-substance,  which 
pass  across  the  intercellular  spaces.  This  is  especially  the  case  with 
the  cells  of  the  higher  plants,  but  it  has  also  been  found  to  occur  in 
animal  tissues,  as  in  some  varieties  of  epithelium  and  in  cardiac  and 
plain  muscular  tissue.  Occasionally  the  connexion  of  the  cells  of  a 
tissue  is  even  closer,  and  lines  of  separation  between  them  are 
almost  or  entirely  absent.  The  term  syncytium  is  given  to  any  such 
united  mass  of  cells. 


Fig.  1.— Diagram  of  a  cell,  highly  m.\gnified. 
p,  protoplasm,  consisting  of  hyaloplasm  and  a  network  of  spongioplasm ;  ex,  exoplasm  ; 
end,  endoplasm,  with  distinct  granules  and   vacuoles  ;   r,   double   centrosome ;   n, 
nucleus  ;  n',  nucleolus. 

Cells. — A  cell  is  a  minute  portion  of  living  substance  {cytoplasm)^ 
which  is  sometimes  inclosed  by  a  cell-membrane  and  always  contains  a 
specially  differentiated  part  which  is  known  as  the  nucleus. 

The  cytoplasm  of  a  cell  (fig.  \,  p)  is  composed  of  protoplasm,  which 
consists  chemically  of  proteid  or  nucleoproteid  substances,  with  which 


STRUCTURE   OF  THE   CELL.  3 

lecithin,  a  combination  of  fatty  acid  with  glycerophosphoiic  acid, 
and  cholesienn,  a  monatomic  alcohol,  having  many  of  the  physical 
characters  of  fats,  appear  always  to  be  associated.     The  protoplasm 


V 


w 


5 

Fig.  2. — Successive  changes  exhibited  by  ax  amceba.     (Verworn.) 

tends  during  life  to  exhibit  movements  which  are  apparently  spon- 
taneous, and  when  the  cell  is  uninclosed  by  a  membrane  a  change 
in  the  shape,  or  even  in  the  position  of  the  cell,  may  be  thereby 
produced.  This  is  characteristically  shown  in  the  movements  of  the 
unicellular  organism  known  as  the  amceba  (fig.  2)  ;   hence  the  name 


Fig.  3. — Protoplasjiic  strl'cture  in  a  pseudopodidm  of  a  foraminifer 
(miliola).     (Verworn,  after  Biitschli. ) 

amoeboid  movement,  bj'^  which  it  is  generally  designated.^  The  proto- 
plasm often,  but  not  always,  contains  a  fine  spongework,  which 
takes  under  high  powers  of  the  microscope  the  appearance  of  a 
network  (figs.  1,   3),   the  remainder  of  the  protoplasm  being  a  clear 

^The   amoeboid   phenomena   of  cells   will  be  studied  later  (in  the   colourless 
corpuscles  of  blood). 


THE   ESSENTIALS   OF  HISTOLOGY. 


■•*«-*.- 


substance   which    occupies   the   interstices   of   the   sponge,    and   may 
also  cover  the  surface  or   project  beyond   the   rest   of  the   cell.     A 

granular  appearance  is  often  produced  by 
the   knots  in  the  network  when  imper- 
fectly   observed    looking    like     separate 
granules.     The  material  which  forms  the 
reticulum    is    termed   spongioplasni ;    the 
A  V'*">."'   ':^.f'ti^^t'^^     clearer  material  which  occupies  its  meshes 
*       ^"^     ;;■*    ^''*'       ;        is  hyaloplasm.      The  protoplasm  of  some 
^  ^:         .  ,*  cells    shows    a    considerable    degree    of 

.    *'j,. '-  differentiation  into  fibrils  which  may  be 

W"^  -  unbranched    or    may    form    a    network 

^      .     „  ,  within   the   cell.      Some   cells   exhibit  a 

Fig.  4.— Troi'hosi'()N(jium  (canal- 
isation) WITHIN  A  GANGLION  fine     caualisatiou     of    their     protoplasm 
CELL.       .     omgren.)  ^^^^  ^^^  ^^^  according  to  Holmgren  the 

canaliculi  are  in  many  cases  occupied  by  branching  processes  of  other 
(nutrient)  cells,  which  form  what  he  terms  a  "trophospongium." 
Protoplasm   often,    if    not   always,    includes   actual   granules   of    a 


,'*^A,' 


Fig.  5.— Cells  from  the  testicle  of  the  mouse  in  process  of  transfor- 
mation INTO  spermatozoa.     (Benda.) 

The  "mitochondria"  are  darkly  stained  and  are  seen  in  the  successive  stages  (a  to  y)  to 
be  arranging  themselves  so  as  to  constitute  the  spiral  filament  of  the  spermatozoon 
{h). 

proteid    nature.     Some    of    these    granules    may    be    essential    con- 
stituents of  the  protoplasm  (Altmann) ;    others  are  materials  which 


STRUCTURE   O?^  THE   CELL.  5 

have   been   formed    by    the   protoplasm,    and    which   are   in   a   sense 

accidental   inclusions.     That   the   former   are   of  importance   appears 

to  be  evident  from  the  fact   that   many  of  the   chemical  changes  of 

cells  occur  in  them.     Moreover  they  are  closely  associated  with  the 

most    active    part    of    the    protoplasm,    the    part,    namely,    in    the 

neighbourhood   of    the   nucleus,    and    appear    to    become   formed   in 

this   part,    and   from   it    to   extend   through    the  cell.     When   fibrils 

are   formed   in   the    protoplasm,    they    are   believed   to   be   produced 

from  the  granules  in  question,  to  which 

the    name    mitochondria    has    been    given 

(Benda),  (fig.  5).     The  mitochondria  are 

sometimes  collected  into  a  spherical  mass 

near    the    nucleus    which     stains     more 

deeply  than  the   rest   of  the    cytoplasm 

(fig.  6).      To   this   body  the  term  pam- 

imcleus  has  been  applied.     The  granules 

referred   to  may  be   regarded  as   actual 

constituents  of  the  cytoplasm,  and  formed   Fig.  6.— Pancreas  cells  of  frog, 

■,•  ,1        n  ..  ,1  i        •       T        ,  SHOWING         PARANUCLEUS        AXD 

directly  from  Its  protoplasm.     As  indicat-      choxdromitome  fibrils  formed 
ing  this  close  connexion  with  protoplasm       ^^?\  ^"tochoxdria.       (Gur- 

'^  _  '^  '■  witsch,  after  Matthews.) 

they  may  conveniently  be  termed  deufo- 

plasm.  This  name  has  also  been  used  to  include  materials  which 
are  merely  included  in  the  cytoplasm  and  not  factors  in  its  constitu- 
tion, such  as  pigment  granules,  fat  globules,  and  vacuoles  containing 
watery  fluid,  with  or  without  glycogen  or  other  substances  in  solution. 
Materials  M'hich  are  thus  included  in  the  protoplasm  of  a  cell  are 
either  stored  up  for  the  nutrition  of  the  cell  itself,  or  are  converted 
into  substances  which  are  eventually  extruded  from  the  cell  in  order 
to  serve  some  purpose  useful  to  the  whole  organism,  or  to  be 
got  rid  of  from  the  body.  The  term  ixiraplasm  may  be  employed 
to  denote  any  such  materials  within  a  cell.  Paraplasm  is  often 
present  in  sufficient  quantity  to  reduce  the  cytoplasm  to  a  relatively 
small  amount,  the  bulk  of  the  cell  being  occupied  by  other  material,  as 
when  starch  becomes  collected  within  vegetable  cells  or  fat  within 
the  cells  of  adipose  tissue.  It  is  frequently  the  case  that  the  para- 
plasm and  deutoplasm  are  confined  mainly  to  the  middle  of  the 
cell  in  the  neighbourhood  of  the  nucleus,  an  external  zone  of  the 
protoplasm  being  left  clear.  The  two  portions  of  protoplasm  which 
are  thus  somewhat  imperfectly  differentiated  off  from  one  another 
are  termed  respectively  the  endoplasm  and  the  exoplasm  (fig.  1). 
They  are  exhibited  in  the  amoeba  (fig.  2),  and  also  in  the  white 
blood-corpuscle  (fig.  8). 


6  THE   ESSENTIALS   OF   HISTOLOGY 

According  to  the  view  advocated  by  Blitschli  the  apparent  reticulum  or 
spongioplasm  of  a  cell  is  the  optical  effect  of  a  soft  honeycomb  or  froth-like 
structure :  in  other  words,  the  meshes  of  the  reticulum  do  not  communicate 
with  one  another  as  in  a  sponge,  but  are  closed  cavities  as  in  a  honeycomb. 
Blitschli  finds  indications  of  the  same  alveolar  structure  in  all  cells,  including 
nerve-fibres  and  muscle-fibres,  and  has  devised  experiments  with  drops  of 
froth  made  up  of  a  mixture  of  oil  and  alkaline  cai'bonate  or  sugar  solution, 
which,  when  examined  in  water  under  the  microscope,  imitate  very  closely 
not  only  the  structural  appearance  (fig.  7)  but  even  the  so-called  spontaneous 


Fig.  7. — Comparisox  of  protoplasm  with  oil  and  water  emulsiox. 

A ,  Protoplasm  of  Thalassicola. 

B.  Froth-like  appearance  of  a  mixture  .of  oil  and  cane  sugar.     (Verwora,  after  Blitschli.) 

or  amceboid  movements  of  actual  protoplasm.  It  may  be  stated,  however, 
that  although  it  is  a  matter  of  difficulty  to  determine  whether  a  microscopic 
reticulum  is  a  sponge-work  or  a  honeycomb,  it  is  probable  that  neither 
><tructure  is  essential  to  living  substance,  for  the  outermost  layer  of  the  cell 
protoplasm,  which  is  usually  the  most  active  in  exhibiting  movements,  often 
shows  no  indication  of  such  .structure.  And  further,  it  has  been  shown  bv 
Hardy  that  a  colloid  solution  such  as  that  which  exists  in  protoplasm  may, 
under  some  circumstances,  appear  homogeneous  and  under  others  may 
separate  out  into  two  parts,  one  more  solid  the  other  more  fluid,  and  after 
.such  separation  may  exhibit  either  a  granular,  a  reticular,  or  a  honeycomb 
structure,  according  to  circumstances.  Xor  is  a  "froth"  necessary  for  the 
imitation  of  amoeboid  movements,  for  similar  movements,  due  to  changes  in 
surface  tension,  are  brought  about  in  a  simple  oil  drop  or  in  a  drop  of 
oil-clad  albumen  when  brought  in  contact  with  solution  of  soap  or  of  any 
alkali  (Berthold,  Quincke).  A  ch'op  of  any  colloid  solution  containing 
electrolytes  is  also  subject  to  such  changes  of  surface  tension  when  exposed 
to  varying  electrical  influences,  so  that  these  amoeboid  movements,  which 
are  certainly  "  vital,"  are  capable  of  being  explained  by  well-known  physical 
laws 

There  are  grounds  for  belie\-ing  that  a  very  fine  pellicle  covers  the  exterior 
of  the  protoplasm  of  all  free  cells,  and  that  this  pellicle  is  composed  of  a 
material  which,  although  not  .soluble  in  water,  is  permeable  to  watery  fluids, 
and  may  also  allow  the  passage  of  solids  without  rupture.  Such  a  material 
might  be  furnished  by  the  lecithin  and  cholesterin  (Overton),  which  are,  as 
we  have  seen,  constant  constituents  of  cell-protoplasm.  It  must,  however, 
be  stated  that  it  has  not  been  proved  that  these  substances  are  collected  at 
the  surface  of  jnotoplasm. 

Properties  of  living  matter. — Living  cells  exhibit  (1)  irritability  or  the 
property  of  responding  to  stimuli  ;  (2)  metabolic  or  chemical  changes  which 
result  in  assimilation  or  the  taking  in  of  nutrient  matter  and  converting  it 
into  living  substance  (anabolism),  and  disassimilation^  the  property  of  break- 


STRUCTURE   OF  THE  CELL.  7 

ing  down  or  getting  rid  of  such  substance  (katabolism) ;  (3)  reprodwition 
resulting  in  the  multiplication  of  cells.  Of  these  properties  (2)  and  (3)  are 
certainly  governed  or  influenced  by  the  cell-nucleus,  and  (3)  appears  to  be 
usually  initiated  by  the  centrosome  (see  below).  The  irritability  of  the  cell 
ilepends,  however,  mainly  upon  the  cytoplasm  itself.  It  is  in  consequence  of 
this  pro|)erty  that  protoplasm  reacts,  sometimes  by  contraction  sometimes 
by  relaxation,  to  mechanical,  chemical,  thermal,  and  electrical  stimuli,  and  in 
the  case  of  some  cells  {e.g.  the  pigment-cells  and  cones  of  the  retina)  to  the 
stimulus  of  light.  The  amoelwid  movements  of  cells  are  a  manifestation  of 
irritability,  being  produced  and  influenced  by  various  external  conditions 
and  stimuli.  Sometimes  the  result  of  a  stimulus  is  to  cause  a  cell  or  organism 
to  move  towards  the  source  of  excitation  (attraction)  ;  in  other  cases  the 
movement  is  in  the  reverse  direction  (repulsion).  The  terms  positive  and 
negative  chemotaxis,  phototaxis,  thermotaxis,  and  the  like,  are  used  to  indi- 
cate the  nature  of  the  effects  produced  by  various  forms  of  stimulation. 

Attraction-sphere  and  centrosome. — In  some  cells,  as  already  indi- 
cated, there  are  line  but  distinct  striae  or  fibrils  (cytomifome)  running 
in  definite  directions.     These  are  very  commonly  met  with  in  fixed 


Fig.  8. — An   amceboid   cell    (white      Fig.   9. — A  cell   (white  bloodcorpuscle) 


CORPUSCLE    OF    XEWT)    VERT    HIGHLY 

MAG.MFIED. 
Showing  a  double  nucleus  with  recticulum 
of  chromoplasm,  and  the  protoplasm  com- 
posed of  two  iwrtions,  a  clearer  exoplasm, 
and  a  gi-anular-looking  eudoplasm. 


SHOWING    ITS    ATTRACTION-SPHERE. 

(Wilson,  after  M.  Heidenhain.) 

In  this,  as  in  most  cases,  the  attraction-sphere,  a, 

lies  near  the  nucleus,  n. 


cells,  such  as  various  kinds  of  epithelium-cells,  nerve-cells,  and  muscle- 
cells.  But  besides  these  special  differentiations,  which  appear  to  be 
related  to  special  functions,  there  are  other  fibril-like  structures  in  the 
cell-protoplasm,  associated  with  what  is  known  as  the  centrosome  (figs. 
1,  9).  This  is  a  minute  particle  (centriole),  usually  situated  near  the 
nucleus,  and  staining  darkly  with  iron-haematoxylin,  surrounded  by 
a  clear  area  (attraction-sphere),  and  from  it  jadiate  into  the  surround- 
ing protoplasm  a  number  of  fine  fibrils  with  dot-like  enlargements 
at  intervals.  The  attraction-sphere,  Avith  its  central  particle,  was 
first  noticed  in  the   ovum  and  was  at  first  supposed  to  be  peculiar 


8  THE   ESSENTIALS   OF   HISTOLOGY. 

to  the  egg-cell,  but  it  has  now  been  recognised  in  very  many  kinds 
of  cells,  and,  in  animal  cells,  is  of  nearly  universal  occurrence.  The 
structures  in  question  are  frequently  double  (fig.  1),  the  twin  spheres 
being  connected  by  a  spindle-shaped  system  of  delicate  fibrils 
{acliromatic  sjnndle) :  this  duplication  invariably  precedes  the  division 
of  a  cell  into  two. 

In  some  cells  the  centrioles  are  multiple  ;  this  is  frequently  the  case  with 
leucocytes  and  always  with  the  giant-cells  of  bone  marrow."  The  material 
which  immediately  surrounds  the  centrosome,  and  of  which  the  radiating 
fibres  and  the  fibres  of  the  s])indle  are  composed,  is  considered  by  some  to 
be  distinct  in  nature  from  the  general  protoplasm  :  it  has  been  termed 
the  archoplasm.  It  appears  clear  tliat  in  some  cells  the  centrosome  and 
archoplasm  may  have  an  existence  independent  of  one  another;  thus  no 
centrosome  has  been  found  in  the  cells  of  the  liigher  plants,  although  the 
avchoplasmic  fibres  are  very  well  marked  in  them  during  cell-division. 

A  cell-membrane  is  rarely  distinct  in  animal  cells.  When  present, 
it  is  usually  formed  by  transformation  of  the  external  layer  of  the 
protoplasm,  but  its  chemical  nature  has  not  been  suflficiently  investi- 
gated.    In  plant  cells  a  cellulose  membrane  is  of  common  occurrence. 

The  nucleus  of  the  cell  (fig.  1,  n)  is  a  small  vesicle,  spherical, 
ovoid,  elongated,  annular,  or  irregularly  lobulated  (figs.  8,  9,  10), 
embedded  in  the  protoplasm.  Cells  have  sometimes  two  or  more  nuclei. 
The  nucleus  is  bounded  by  a  membrane  which  incloses  a  clear  sub- 
stance (miclear  hi/aloplasm,  karpoplasm),  and  the  whole  of  this  substance 
is  generally  pervaded  by  an  irregular  network  of  fibres,  some  coarser, 
others  finer  {nuclear  reticuhim,  hiryomitome).  The  membrane  is  the 
outermost  layer  of  the  nuclear  reticulum,  and  may  itself  have  meshes 
like  a  basket-work,  thus  allowing  direct  communication  between  the 
hyaloplasm  of  the  cell  and  that  of  the  nucleus.  The  knots  of  the 
nuclear  reticulum  are  sometimes  very  distinct  and  give  an  appearance 
of  conspicuous  granules  within  the  nucleus  {pseudonucleoli).  The  nucleus 
usuall)'  contains  a  single  distinct  highly  refracting  spherical  particle 
known  as  the  nucleolus.  This  is  sometimes  multiple,  and  occasionally 
has  a  vacuole-like  globule  in  its  interior.  The  material  of  the  nucleolus 
diflPers  in  its  chemical  and  staining  reactions  from  the  nuclear 
reticulum,  but  prior  to  cell-division  it  becomes  indistinguishable 
from  the  substance  of  the  nuclear  fibres.  Whether  it  blends  with 
them  or  becomes  absorbed  and  removed  is  at  present  uncertain.  The 
nuclear  membrane,  intranuclear  fibres,  and  nucleoli  all  stain  deeply 
with  haematoxylin  and  with  basic  dyes  generally ;  this  property  distin- 
guishes them  from  the  nuclear  matrix,  and  they  are  accordingly  spoken 
of  as  chromatic  (containing  chromatin,  which  in  the  nucleus  appears  to 
be  chemically  identical  with  nnclein),  the  hyaloplasm  being  achromatic. 
Sometimes  instead  of  beine  united   into  a  network  the  intranuclear 


STRUCTURE   OF  THE   CELL. 


9 


fibres  take  the  form  of  convoluted  filaments  (rhromosomes),  having  a 
skein-like  arrangement  (fig.  11).  This  is  always  found  when  a 
nucleus   is   about   to    divide,    but    it    may  also   occur   in   the  resting 


Fig.  10. — Cell  from  bone-marrow. 
(Carnoy.) 

p,  protoplasm  with  fine  reticulum;  v, 
nucleus,  long  and  folded,  with  intra- 
nuclear network. 


Fig.  11.— Gland-cell  of  Chirono- 
MU.s.     (Flemming.) 


condition.  These  filaments  may  sometimes  be  seen  with  high  magni- 
fication to  be  made  up  of  fine  juxtaposed  particles  (chromomeres) 
arranged  either  in  single  or  double  rows  (fig.  12),  which  impart  a 
cross-striated  appearance  to  the  filament.  The  chromomeres  are 
united  to  form  the  chromosomes  by  a  non-staining  material  to  which 


4  Wi*i^*^««^ 


Fig.  12.— Spermatocyte  of  pkoteus,  showing  chromosomes  of  nucleus 

formed  of  particles  op  chromatin  united  by  acromatic  filaments. 

(Giirwitsch,  after  Hermann.) 

The  nucleolus  is  distinct  from  the  chromosomes.     In  the  cytoplasm  an  archoplasmic 
mass  containing  mitochondria  is  seen  on  the  right. 

the  term  linin  has  been  applied.  The  nuclear  fibres  are  sometimes 
clumped  together  into  a  solid  mass  which  comprehends  the  nucleolus 
when  present,  and  has  the  appearance  of  an  enlarged  nucleolus.     The 


10 


THE   ESSENTIALS  OF  HISTOLOGY. 


fibres  within  the  nucleus  have  been  observed  to  undergo  spontaneous 
changes  of  form  and  arrangement,  but  these  become  much  more 
evident  during  its  division.  The  division  of  the  protoplasm  is 
always  preceded  by  that  of  the  nucleus,  and  the  nuclear  fibres 
undergo  during  division  a  series  of  remarkable  transformations  which 
are  known  collectively  by  the  term  hni/okinesis  (Schleicher)  or  mitosis 
(Flemming).  These  changes  may  easily  be  studied  in  the  division  of 
epithelium  cells,  but  exactly  similar  phenomena  have  been  shown  to 
occur  in  cells  belonging  to  other  tissues. 


Fig.  13. — Cell  of  bladder  epithelium,  showing  amitotic  division  of 
NUCLEUS.     (Nemileff.) 

/.  cj'toplasm  ;  //.  daughter  nuclei  ;  ///.  strand  of  fibrils  uniting  daughter  nuclei. 

The  simple  division  of  a  nucleus  by  a  process  of  fission  without 
karyokinetic  changes  is  termed  amitotic  division :  it  occurs  in  com- 
paratively rare  instances,  and  is  not  usually  followed  by  the  division 
of  the  cell,  so  that  it  is  apt  to  result  in  the  formation  of  bi-nucleated 
and  multi-nucleated  cells,  as  in  the  superficial  layer  of  the  epithelium 
of  the  urinary  bladder  and  in  some  of  the  giant  cells  of  bone-marrow. 

The  nucleus  of  the  cell  is  not  only  concerned  with  its  division  and 
multiplication  in  the  manner  shown  below,  but  takes  an  active  part 
in  the  chemical  (metabolic)  processes  which  occur  in  the  protoplasm. 
Hence^  cells  depriA'ed  artificially  of  their  nuclei  do  not  assimilate 
nourishment,  and  lose  any  power  of  secretion  they  may  have 
possessed,  although  the  protoplasm  may  continue  for  a  time  to  live 
and  exhibit  amoeboid  movements. 


DIVISION   OF  CELLS.  11 

Division  of  cells. — The  division  of  a  cell  is  preceded  l)y  the  division 
of  its  attraction-sphere,  and  this  again  appears  to  determine  the 
division  of  the  nucleus.  The  latter,  in  dividing,  passes  through  a 
series  of  remarkable  changes,  which  may  thus  be  briefly  summarised 


Fig.  14. — Epithelium-cells  op  salamandra  larva  in  different  phases  of 
DIVISION  BY  karyokinesis  OR  MITOSIS.     (Flemming.) 


as  they  occur  in  typical  animal  cells  such  as  the  epithelium  cells  of 
Salamandra : — 

1.  The  network  of  chromoplasm-filaments  of  the  resting  nucleus 
becomes  transformed  into  a  sort  of  skein,  formed  apparently  of  one 
long  convoluted  filament,  but  in  reality  consisting  of  a  number  of 
filaments  (spirem) ;  the  nuclear  membrane  and  the  nucleoli  disappear 
or  are  merged  into  the  skein  (fig.  14,  a  to  d). 

2.  The  filament   breaks  into  a  number  of  separate  portions,  often 


12 


THE   ESSENTIALS   OF  HISTOLOGY 


V-shaped,  the  chromosomes.  The  number  of  chromosomes  varies  with 
the  species  of  animal  or  plant ;  in  some  animals  the  dividing  nuclei 
may  contain  at  this  stage  only  four  chromosomes ;  in  man  there  are 
said  to  be  twenty -four  in  the  ordinary  or  somatic  cells ;  a  like 
number  occurs  in  many  animals  and  plants :  others  have  more 
or  fewer.  As  soon  as  the  chromosomes  become  distinct  they  are 
often  arranged  radially  around  the  equator  of  the  nucleus  like  a 
star  {(ister,  fig.  14,  e,  f,  g). 


Fig.  15. — The  prinx'ipal  ph.\ses  of  the  nuclear  chromatin  filaments  in  the 
PROCESS  OF  ordinary  jiitosis  OF  THE  SOMATIC  CELL.     (Flemming.) 

A,  skein  or  spirem  ;  B,  aster  with  splitting  of  chromosomes  ;  C,  separation  of  the  split 
chromosomes  (metakinesis) ;  D,  continuation  of  this  process ;  JF,  diaster ;  F,  di- 
spirem.  The  cell  protoplasm  is  represented  in  oiitline  in  F:  it  has  itself  undergone 
division  at  this  stage.  In  this  figure  the  (somatic)  cells  represented  are  supposed 
to  have  eight  chromosomes. 

3.  Each  of  the  chromosomes  splits  longitudinally  into  two,  so  that 
they  are  now  twice  as  numerous  as  before  (stage  of  cleavage,  fig.  14, 
h,  i).     This  longitudinal  cleavage  may  occur  at  an  earlier  stage. 

4.  The  fibres  separate  into  two  groups,  the  ends  being  for  a  time 
interlocked  (fig.  14,  /,  k). 

5.  The  two  groups  pass  to  the  opposite  poles  of  the  now  elongated 
nucleus  and  form  a  star-shaped  figure  at  either  pole  {diaster,  fig.  14,  I). 
Each  of  the  stars  represents  a  daughter  nucleus. 

6.  7,  8.  Each  star  of  the  diaster  goes  through  the  same  changes  as 
the  original  nucleus,  but  in  the  reverse  order — viz.  a  skein,  at  first 
more  open  and  rosette-like  (fig.  14,  m),  then  a  closer  skein  (fig.  14,.  n). 


DIVISION   OF   CELLS. 


13 


^W- 


E    ^^ 


^«^*    ^i}» 


Fig    1(5.-Hetero-typical  axd  homo-typical  mitosis  of  the 

GENERATIVE  CELL.     (Flemmmg.) 

The  asterisk  marks  the  middle,  the  cross  the  end  of  a  chromosome. 

The  changes  are  to  be  compared  with  tl^ose  shown  in  fig^  15.    ^- ^^^^^^tmrn^^cef /^s 
the  chromosomes  are  already   arranged  in  pairs   betore  f^'",'''"  hc  prophase, 

condition  (geminal  condition,  f,  ^Ser'''sU<^rand  the  daughteV  nSc^ei^         the 
A  longitudinal  split  is  seen  in  ^f  Piaster  stgo^ndtUeaag  .^^  j^^.^ 

somatic  iiumber  of   chromosomes  0>  in  «nsm.^^^^^^  ^^^  separation  to 

Sthe-^L^ghfel  nucfe^  rL^^ultf  in^a  i^dS  to  one-half  the  somatic  number. 


14 


THE   ESSENTIALS  OF   HISTOLOGY. 


then    a    network    (fig.    14-,   o,  p,  q) ;    passing    finally    into    the    typical 
reticular  condition  of  a  resting  nucleus. 


Fig.  17.— Spermocttes  of  salamaxdra  showing  V-shaped  chromosomes 
AT  THE  EQUATOR  OF  THE  SPINDLE.     (Wilson,  after  Drliner.  j 

A,  seen  in  profile  ;  four  chromosomes  only  arc  represented. 

B,  seen  end-on.     All  twenty-four  chromosomes  are  represented ;  the  fibrils  of  the  spindle 

are  seen  in  optical  section. 


The  splitting  and  separation  of  the  chromosomes  is  often  spoken  of  as  the- 
onetaphase  {metakinesis)  ;  the  stages  leading  up  to  this  beiug  termed  the 
anaphase  and  those  by  which  the  process  is  terminated  the  katapha.se  or 
telophase. 

The  mode  of  division  of  the  nuclear  chromatin  above  described  is 
frequently  spoken  of  as  somatic  or  orcUna.ry  mitosis  (fig.  15)  to  distinguish 
it  from  two  modes  of  division  which  are  only  seen  normally  at  certain  stages 
of  multiplication  of  the  generative  cells,  and  which  are  known  as  hetero- 
typical  and  homotypical  mitosis  (fig.  16).  In  the  latter  the  chromosomes  do 
not  undergo  the  usual  longitudinal  S23litting,  but  one  half  of  the  total  number 
passes  into  each  daughter  nucleu.*,  so  that  the  number  of  chromosomes  iu 
each  of  these  is  only  one  half  the  usual  somatic  number.  This  is  termed 
the  reduction-division}  Heterotypical  mitosis  (which  immediately  precede* 
the  homotypical)  is  characterised  by  a  peculiar  arrangement  of  the 
chromosomes,  tlie  split  halves  of  which,  before  sejjarating  to  pass  to  the 
daughter  nuclei,  tend  to  adhere  together  in  the  forul  of  loops  or  rings,  or 
in  the  case  of  short  straight  chromosomes  into  small  quadrangular  masses 
(tetrads),  all  of  which  are  observable  in  various  instances  of  heterotypical 
mitosis,  (see  fig.  19). 

It  is  further  noteworthy  that  the  generative  cells  which  later  undergo  the 
reduction-division  above  described  exhibit  either  immediately  (sperm-cells) 
or  a  long  while  (germ-cells)  before  the  maiotic  divisions  a  remarkable 
series  of  changes  in  their  nuclear  chromatin  ;  the  chi-omosomes  becoming  first 
distinct  in  place  of  forming  a  network,  then  entangled  together  at  one  side 
of  the  nucleus  (synaptic  condition),  and  finally  becoming  again  distinct,  but 
now  arranged  in  pairs  (gemini)  which  later  take  various  forms,  such  as 
double  rods,  loops,  or  rings  as  in  heterotypical  mitosis,  but  without  forth- 
with proceeding  to  nuclear  division. 

The  protoplasm  of  the  cell  divides  soon  after  the  formation  of  the 
diaster  (fig.  14,  m).     During  division  fine  lines  are  seen  in  the  proto- 

^  "Maiotic  division"  or  "maiosis"  of  Farmer,  Moore  and  Walker. 


DIVISION   OF   CELLS. 


15 


plasm,  radiating  from   tlie  cetitrosomes  at  the   poles  of   the  nucleus, 
whilst  other  lines  form  a  spindle-shaped   system   of   achmnatir  Hhi-es 


;     1   ^ 


VI. 


VII. 


VIII. 


Fie     18  -Diagram  showing   the   changes   which   occur  in  the  centro- 

■  SOMES   and   nucleus   OF  A   CELL  IN   THE   PROCESS    OF   MITOTIC    DIVISION. 
The  nucleus  is  supposed  to  have  four  chromosomes. 

within   the    nucleus,    diverging   from   the   poles  towards  the  equator 
(fig.  18).     These  are  usually  less  easily  seen  than  the  chromatic  fibres 


16 


THE   ESSENTIALS   OF  HISTOLOGY. 


or  chromosomes  already  described,  but  are  not  less  important,  for 
they  are  derived  from  the  attraction-spheres.  These,  with  their 
centrosomes,  as  we  have  -seen,  always  initiate  the  division  of  the 
cell ;  indeed  they  are  often  found  divided  in  the  apparently  resting 
nucleus,  the  two  particles  being  united  by  a  small  system  of  fibres 
forming  a  minute  spindle  at  one  side  of  the  nucleus  (fig.  1).  When 
mitosis  is  about  to  take  place  this  spindle  enlarges,  and  as  the 
changes   in   the   chromatin   of  the   nucleus    which    have   been   above 


Fig.  19. — Thkek  stages  of  heterotype  mitosis  in  spermatocyte  of 
TRITON.     (Moore.) 

a,  geminal  condition  of  ehroniosomes  ;  h,  gemini  arranged  in  quadrate  loops  or  tetrads  ; 
c,  separation  of  tetrads  into  the  duplex  chromosomes  of  the  daughter  nuclei. 

described  occur — which  changes  involve  the  disappearance  of  the 
nuclear  membrane — the  spindle  gradually  passes  into  the  middle  of 
the  mitotic  nucleus,  with  the  two  poles  of  the  spindle  at  the  poles  of 
the  nucleus,  and  with  the  fibres  of  the  spindle  therefore  completely 
traversing  the  nucleus  (fig.  18).  The  spindle-fibres  appear  to  form 
directing  lines,  along  which  the  chromosomes  pass,  after  the  cleavage, 
towards  the  nuclear  poles  to  form  the  daughter  nuclei. 

In  some  cells,  especially  in  plants,  the  line  of  division  of  the  proto- 
plasm of  the  cell  becomes  marked  out  by  thickenings  upon  the  fibres 
of  the  spindle  which  occur  just  in  the  plane  of  subsequent  division, 
and  have  been  termed  collectively  the  cell-plate  (fig.  20).  But  in 
most  animal  cells  no  cell-plate  is  formed,  the  protoplasm  simply 
becoming    constricted    into    two    parts    midway    between    the    two 


DIVISION   OF  CELLS. 


17 


daughter  nuclei.  Each  chuightcr  coll  so  fonued  retains  one  of  the 
two  attraction-particles  of  the  spindle  as  its  centrosome,  and  when 
the  daughter  cells  are  in  their  turn  again  about  to  divide  this  centro 
some  divides  first  and  forms  a  new  spindle,  and  the  whole  process 
goes  on  as  before. 


^^i_.^' 


Fig 


20. — Cell-plate  ix  dividing 
spore-cell  of  lilt. 
(Gurwitsch,  after  Zimmermann.) 


Fig.  21. — Dividing  cell  constricted 
to  form  two  daughter  cells  each 

WITH   CENTROSOME.       (Gebei'g.) 
The  particle  at  the  junction  of  the  daughtei- 
cells  represents  a  rudimentary  cell-plate. 


Earely  the  division  of  a  nucleus  is  into  three  or  more  parts  instead  of 
two.  In  such  cases  the  centrosome  becomes  correspondingly  multiplied  and 
the  achromatic  system  of  fibres  takes  a  more  complex  form  than  the  simple 
spindle. 

Division  of  the  Ovum. — Usually  the  two  daughter  cells  are  of 
equal  size ;  but  there  is  a  notable  exception  in  the  case  of  the  ovum, 
which,  prior  to  fertilisation,  divides  twice  (by  hetero-  and  homotypical 
mitosis  respectively)  into  two  very  unequal  parts,  the  larger  of  which 
retains  the  designation  of  ovum,  while  the  two  small  parts  which 
become  detached  from  it  are  known  as  the  jyolar  bodies  (fig.  22). 
Further,  in  the  formation  of  the  second  polar  body  a  redudion-divimm 
occurs,  and  the  nucleus  of  the  ovum,  after  the  polar  bodies  are 
extruded,  contains  only  one  half  the  number  of  chromosomes  that 
it  had  previously  (e.g.  twelve  in  place  of  the  normal  twenty-four  in 
man,  and  two  instead  of  four  in  Ascaris  megalocephala  (var.  bivalens), 
fig.  22,  C).  Should  fertilisation  supervene  the  chromosomes  which 
are  lacking  are  supplied  by  the  male  element  (sperm-cell),  the  nucleus 
of  which  has  also  undergone,  in  the  final  cell-division  by  which  it  was 
produced,  the  process  of  reduction  in  the  number  of  chromosomes  to 
one  half  the  normal  number.  The  two  reduced  nuclei — which  are 
formed  respectively  from  the  remainder  of  the  nucleus  of  the  oocyte 


18 


THE   ESSENTIALS   OF   HISTOLOGY. 


(ovum)  after  extrusion  of  the  polar  bodies,  and  from  the  head  of 
the  spermatozoon,  which  contains  the  nucleus  of  the  sperm-cell — are 
known  (within  the  ovum)  as  the  sperm  and  germ  nuclei  or  the  male  and 


Fig.  22. —Formation  of  the  polar  glob- 
ules AND   reduction   OF  THE   NUMBER   OF 

chromosomes  in  the  ovum  of  ascaris 
megalocephala. 

A,  B,  ovum  showing  division  of  nucleus  to  form 
first  polar  globule  (Van  Gehuchten).  m,  gelatin- 
ous envelope  of  ovum  ;  m' ,  membrane  dividing 
the  polar  globule  from  tiie  ovum  ;  cs  (in  A), 
head  of  spermatozoon. 

C,  formation  of  second  polar  globule  (Carney) ; 
(/I,  first ;  g~,  second  polar  globule  :  n,  nucleus 
of  ovum,  now  containing  only  two  chromo- 
somes ;  ns,  nucleus  formed  from  head  of  sper- 
matozoon. 


Fig.  23.— Ovum  of  bat  with  polar  bodies  and  germ-  and 
sperm-nuclei.     (Van  tier  Stricht.) 

The  development  of  the  sperm-nucleus  from  the  head  of  the  spermatozoon  is  very 
evident  in  this  case,  because  the  rest  of  the  spermatozoon  happens  not  to  have  been 
thrown  off. 


DIVISION   ()F  THE   OVUM. 


19 


female  pronuclei.     When  these  blend,  the  ovum  again  contains  a  nucleus 
with  the  number  of  chromosomes  normal  to  the  species  (fig.  24,  E). 


Fig.  24. — Fertilisation  and  first  division  of  ovum  of  ascaris  megalo- 
CEPHALA  (slightly  modified  from  Boveri  and  Wilson). 

A,  second  polar  globule  just  formed  ;  the  head  of  the  spermatozoon  is  becoming  changed 

into  a  reticular  nucleus  (^),  which,  however,  shows  distinctly  two  chromosomes; 
just  above  it,  its  archoplasm  is  shown  :  the  egg-nucleus  (J)  also  shows  two  chromo- 
somes. 

B,  both  pro-nuclei  are  now  reticular  and  enlarged ;  a  double  centrosorae  (a)  is  visible 

in  the  archoplasm  which  lies  between  them. 

C,  the  chromatin  in  each  nucleus  is  now  converted  into  two  filamentous  chromosomes  ; 

the  centrosomes  arc  separating  from  one  another. 

D,  the  chromosomes  arc  more  distinct  and  shortened  ;  the  nuclear  meml^ranes  have  dis- 

appeared ;  the  attraction-spheres  are  distinct. 

E,  mingling  and  splitting  of  the  four  chromosomes  (e) ;  the  achromatic  spindle  is  fully 

formed. 

F,  separation  (towards  the  poles  of  the  spindle)  of  the  halves  of  the  split  chromosomes, 

and  commencing  division  of  the  cytoplasm.  Each  of  the  daughter  cells  now  has 
four  chromosomes  ;  two  of  these  have  been  derived  from  the  ovum  nucleus,  two  from 
the  spermatozoon  nucleus. 


20 


THE   ESSENTIALS   OF   HISTOLOGY. 


When  it  divides  after  fertilisation  each  daughter  cell  is  found  to 
contain  the  normal  or  somatic  number  of  chromosomes,  derived  from 
the  splitting  of  both  male  and  female  elements,  half  the  number 
from  the  one  and  half  from  the  other. 


Fig.  25. — Human  ovum  (oocyte)  from  graafian  follicle  :  examined  fresh 

IN   LIQUOR   FOLLICULI   WITH   VERT    HIGH   MAGNIFYING   POWER.       (Waldeyer.) 

The  cells  which  are  attached  to  the  outside,  and  which  appear  to  be  joined  into  a  syn- 
cytium ai'ound  the  ovum,  are  follicular  cells  belonging  to  the  discus  proligerus.  Within 
them  is  the  clear  membrane  of  the  ovum  (zona  pellucida).  The  cytoplasm  of  the 
ovum  shows  a  distinction  between  clear  ectoplasm  and  granular  endoplasm  :  the 
large  granules  are  yolk  particles.  The  nucleus  (germinal  vesicle)  is  clear.  The 
nucleolus  (germinal  spot)  is  distinct. 

Formation  of  the   tissues. — It   appears   to   be  established  beyond 
doubt   that   new  cells    can   only  be   formed   from   pre-existing   cells. 


FORMATION   OF  THE  TISSUES. 
A  ^  B  0 


21 


G 


FIG.    2fi.-FORMATIOK    OF    BLASTODERM    IN    BABBIT    BY  ^I^I^^Oj;^  J^^^^"   '''™ 

A  NUMBER  OF  CELLS.     (Allen  Thomson,  after  E.  v.  Beneden  ) 
A\c^■R  division  of  ovum  and  formation  of  "mulberry  mass"  :  p  gl,  polar  g^o'^i'l^^ '  "V^ 
^  '"ceVof  primar/division  which  already  show  a  differon^  of  -PPe-aBce     Th  s    a  1 
differentiation  is  not,  however,  accepted  by  ""^f „^"^^°"^^„"^^-    enucida)!*^    subzonal 
ovum  in  subsequent  stages,     zp,  membrane  of  °^Xiwto  the  uterSe  mucous 

SKouId  be  .b»wn  in  t  esteadrng  .U  rouDd  the  inner  ceU.m,». 


22 


THE   ESSENTIALS   OF   HISTOLOGY. 


In  the  early  embryo  the  whole  body  is  an  agglomeration  of  cells. 
These  have  all  been  formed  from  the  ovum  or  egg-cell  (fig.  25),  which, 
after  fertilisation,  divides  first  into  two  cells,  these  again  into  two, 
and  so  on  until  a  large  number  of  cells  (embryonic  cells)  are  pro- 
duced. These  form  at  first  an  outer  clear  stratum  lying  at  the 
surface  (fig,  26  sz)  and  a  darker  granular  mass  attached  to  this 
layer  at  one  part,  but  elsewhere  separated  from  it  by  clear  fluid. 
Eventually  the  cells  of  the  inner  mass  arrange  themselves  in  the 
form  of  a  membrane  {blastoderm)  which  is  composed  of  three  layers. 
These  layers  are  known  respectively  as  the  ectoderm,  mesoderm,  and 
en.toclervi.  The  ectoderm  gives  rise  to  most  of  the  epithelial  tissues 
and  to  the  tissues  of  the  nervous  system ;  the  entoderm  to  the 
epithelium  of  the  alimentary  canal  (except  the  mouth),  and  the  glands 
in  connection  with  it ;  and  the  mesoderm  to  the  connective  and 
muscular  tissues. 


f7?^f^^^'^M^>7??7?7^'^^ 


jZ^f^Si 


'Ml 

Fig.  27.— Section  of  blastoderm  showing  the  commencing  formation  of 
THE  MESODERM.     (Kolliker.) 

(J),  ectoderm  ;  hy,  entoderm  ;  tm,  mesoderm ;  ox,  axial  part  of  ectoderm  with  cells  under- 
going division  (t).     The  mesoderm  is  growing  from  this  part. 


The  tissues  are  formed  either  by  changes  which  occur  in  the  inter- 
cellular substance,  or  by  changes  in  the  cells  themselves  ;  frequently 
by  both  these  processes  combined  amongst  the  cells  which  are  least 
altered  from  their  embryonic  condition  are  the  white  corpuscles  of  the 
blood,  and  these  may  be  regarded  therefore  as  typical  animal  cells. 

The  histogenetical  relation  between  the  three  layers  of  the  blasto- 
derm and  the  several  tissues  and  organs  of  the  body  is  exhibited  in  the 
following  table : — 

.The  epithelium  of  the  skin  or  epidermis,  and  its  appendages,  viz.,  the  hairs,  nails, 

sebaceous  and  sweat  glands,  and  mammarj'  glands. 
The  epithelium  of  the  mouth,  and  the  epithelium  of  the  anus  and  anal  canal. 
The  salivary  and  other  glaud.*)  which  open  into  the  mouth.     The  enamel  of  the 

teeth.     The  gustatorj'  organs. 
The  epithelium  of  the  lower  part  of  the  urethra  and  vagina. 
The  epithelium  of  the  nasal  passages,  and  of  the  cavities  and  glands  which  open 
Ectoderm   -'         into  them. 

The  epithelium  covering  the  front  of  the  eye.     The  crystalline  lens.     The  retina. 
The  epithelium  lining  the  membranous  labyrinth   of  the  ear.     The  epithelium 

lining  the  external  auditory  meatus. 
The  epithelium  lining  the  central  canal  of  the  spinal  cord,  the  aqueduct  of  Sylvius, 

and  the  fourth,  third,  and  lateral  ventricles  of  the  brain. 
The  tissues  of  the  nervous  system. 
^The  pituitary  body.     The  pineal  gland.     The  medulla  of  the  suprarenal  capsules. 


ORIGIN   OF   THE  TISSUES, 


23 


'The  connective  tissues. 
The  blood-  and  lyiniih-corpuscles. 
The  spk'cii  aiul  other  vascular  and  lymphatic  glands. 

The  oi)itbclial   lining  of  the  heart,    blood-vessels,  lymphatics,   and   serous   mcm- 
Mesoderni.    -  brancs  (endotlielium). 

The  epithelium  of  the  urinifcrous  tubules. 

The  epithelium  of  the  internal  genenitive  organs,  and  the  generative  products  in 
both  sexes. 
I, The  muscular  tissues,  voluntary,  involuntary,  and  cardiac. 

'The  epithelium  of  the  alimentary  canal  (from  the  pharynx  to  the  lower  end  of 
the  rectum)  and  of  all  the  glands  which  open  into  it  (including  the  liver  and 
paiuTcas). 
Entoderm     -i  '^'^  epithelium  of  the  Eustachian  tube  and  cavity  of  the  tympanum. 

■    "^  The  epithuliuin  of  the  larynx,  trachea,  and  bronchi,  and  of  all  their  ramifications. 
The  e|iithuliinn  of  the  pulmonary  alveoli. 
The  thyroid  body.     The  thymus  gland. 
,The  epithelium  of  the  urinary  bladder  and  ureters,  and  of  part  of  the  urethra. 

1  All  the  connective  tissues,  the  endothelium  (mcsotheliurn)  of  the  vascular  system,  and  the 
vascular  and  lymjihatic  glands  are  formed  from  a  special  jiart  of  the  mesoderm  termed  parnhlast 
or  mesenchyme,  which  consists  of  a  syncytium  of  branched  cells  with  a  homogeneous  intercellular 
matrix.  Plain  muscular  tissue  is  for  the  most  part  also  formed  from  mesenchyme,  but  in 
certain  situations,  as  in  the  sweat  glands  and  muscular  tissue  of  the  iris,  it  is  said  to  be  ecto- 
dermal in  origin. 


24 


THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    I. 

USE  OF  THE  MICROSCOPE.     EXAMINATION  OF 
CERTAIN  COMMON  OBJECTS. 


The  requisites  for  practical  histology 
are  a  good  compound  microscope  ;  slips 
of  glass  technically  known  as  '  slides,' 
upon  which  the  preparations  are  made  ; 
pieces  of  thin  glass  used  as  covers  for 
the  preparations  ;  a  few  instruments, 
such  as  a  microtome,  a  scaljael,  scissors, 
forceps,  and  needles  mounted  in  wooden 
handles  ;  and  a  set  of  fluid  re-agents 
for  mounting  and  staining  microscopic 
preparations.^  A  sketch-book  and  pencil 
are  also  necessary,  and  must  be  constantly 
employed. 

The  microscope  (fig.  28)  consists  of  a 
tube  {t  t')  160  millimeters  (6"4  inches)  long 
having  two  systems  of  lenses,  one  at  the 
upper  end  tei'raed  the  'eye-piece'  or 
'ocular'  {oc),  the  other  at  the  lower  end 
termed  the  '  objective '  {ohj).  For  ordi- 
nary work  there  should  be  at  least  two 
objectives — a  low  power  working  at  about 
8  millimeters  (^  inch)  from  the  object, 
and  a  high  power,  having  a  focal  dis- 
tance of  about  3  millimeters  (^  inch)  ; 
it  is  useful  also  to  have  a  lower  power 
(commanding  a  larger  field  of  view)  for 
finding  objects  readily,  and  two  or  more 
oculars  of  different  power.  The  focus 
is  obtained  by  cautiously  bringing  the 
tube  and  lenses  down  towards  the 
object  by  the  coarse  adjustment,  which 
is  usually  a  rack-and-pinion  movement 
(adj),  and  focussing  exactly  by  the  fine 
adjustment,  which  is  always  a  finely  cut 
screw  (adj). 

The  stage  (st)  upon  which  the  prepar- 
tions  ai'e  placed  for  examination,  the 
mirror  (?h)  which  serves  to  reflect  light 
up  through  the  central  aperture  in  the 
stage  and  along  the  tube  of  the  instrument, 
and   the  diaphragm  (d)  below  the   stage 


Fig 


Diagram  of  mickoscope. 


^  The  directions  for  making  the  principal  fluids  used  in  histological  work  will  be 
found  in  the  Appendix. 


MICROSCOPICAL  EXAMINATION  OF  COMMON  OBJECTS.     25 

which  is  used  to  rej^idate  tlie  amount  of  Ijirht  thus  thrown  up,  are  all 
parts  the  einj)loyuieiit  of  which  is  readily  understood.  A  substat^e  con- 
denser (not  shown  in  the  diagram),  which  serves  to  concentrate  the  light 
thrown  up  by  the  mirror  to  the  centre  of  the  object,  is  valuable  when 
higli  powers  and   stained  preparations  are  employed. 

The  combinations  of  objectives  and  oculars  above  referred  to  will 
generally  give  a  magnifying  power  of  from  .W  to  400  diameters,  and  this 
is  sutticient  for  most  purposes  of  histology.  But  to  bring  out  minute 
points  of  detail  in  the  structure  of  cells  and  of  certain  tissues  examination 
with  much  higher  magnifying  powers  may  be  necessary.  Objectives  of 
higli  power  are  usually  made  as  immersion -lenses  ;  i.e.  they  are  constructed 
to  form  a  proper  image  of  the  object  when  the  lowermost  lens  of  the 
system  is  immersed  in  a  layer  of  li(iuid  which  lies  on  the  cover-glass  of 
the  object  and  has  a  refractive  index  not  far  removed  from  that  of  the 
glass  itself.  For  this  purpose  either  water  or  an  essential  oil  (oil  of  cedar- 
wood)  is  used.  The  advantages  obtained  by  the  employment  of  these  lenses, 
especially  those  for  oil-immersion,  are  : — increased  working  distance  from 
the  object,  increased  angle  of  aperture  with  sharper  definition  of  the  object, 
and  increased  amount  of  light  traversing  the  microscope. 

The  best  lenses  for  histological  work  are  made  of  the  so-called  'apochro- 
matic'  glass  ;  specially  constructed  'compensating'  eye-pieces  are  used  with 
these. 

A  scale  for  measuring  objects  should  be  constructed  for  each  microscope. 
To  do  this,  put  a  stage-micrometer  (which  is  a  glass  slide  ruled  in  the  centre 
with  lines  y\j  and  too  niillimeter  apart)  under  the  microscope  in  such  a 
manner  that  the  lines  run  from  left  to  right  (the  microscope  must  not  be 
inclined).  Focus  them  exactly.  Put  a  piece  of  white  card  on  the  table  at 
the  right  of  the  microscope.  Look  through  the  instrument  with  the  left 
eye,  keeping  the  right  eye  open.  The  lines  of  the  micrometer  will  appear 
projected  upon  the  paper.  Mark  their  apparent  distance  with  jieucil  upon 
the  card,  and  afterwards  make  a  scale  of  lines  in  ink,  of  the  same  interval 
apart.  A  magnified  representation  is  thus  obtained  of  the  micrometer 
scale.  Mark  upon  it  the  number  of  the  eye-piece  and  of  the  objective, 
and  the  length  of  the  microscope-tube.  This  scale-card  will  serve  for  the 
measurement  of  any  object  without  the  further  use  of  the  micrometer. 
To  measure  an  object,  place  the  scale-card  upon  the  table  to  the  right  of 
the  microscope  and  view  the  object  with  the  left  eye,  keeping  the  right 
eye  open.  The  object  appears  projected  upon  the  scale,  and  its  size  in  ^ 
or  Yw  ^f  a  millimeter  can  be  read  off.  It  is  essential  that  the  same 
objective  and  eye-piece  should  be  employed  as  were  used  in  making  the 
scale,  and  that  the  microscope  tube  should  be  of  the  same  length.  The 
lines  on  English  stage-micrometers  are  often  ruled  ^j^  and  i-jpf^o  inch  apart.^ 

Before  beginning  the  study  of  histology  the  student  should  endeavour 
to  familiarise  himself  with  the  use  of  the  microscope,  and  at  the  same 
time  learn  to  recognise  some  of  the  chief  objects  which  are  liable  to  occur 
accidentally  in  microscopic  specimens.  On  this  account  it  has  been  con- 
sidered desirable  to  introduce  directions  for  the  examination  and  recogni- 
tion of  starch-granules,  moulds  and  torulae,  air-bubbles,  linen,  cotton,  and 
woollen  fibres,  and  tlie  usual  constituents  of  the  dust  of  a  room,  into  the 
first  practical  lesson  (fig.  29). 

1.  Examination  of  starch-granules.  Gently  scrape  the  cut  surface  of  a 
potato  with  the  point  of  a  knife  ;  shake  the  starch-granules  so  obtained 
into  a  drop  of  water  upon  a  clean  slide  and  apply  a  cover-glass. 

With  the  low  power  the  starch  granules  look  like  dark  specks  differing 

1  For  the  method  of  measuring  with  an  ocular  micrometer,  and  for  determining 
the  magnifying  power  of  a  microscope,  the  reader  is  referred  to  the  author's 
Course  of  Practical  Histology. 


26 


THE   ESSENTIALS   OF  HISTOLOGY. 


m 

>\ 

-•#^' 

/- 

n 

■4^ 

'.■  \ 

/  \ 

.  1 

y^y^ 

"^ 

-i^ 

Fig.  29.— Objects  frequently  present  in  microscopic  preparations. 

1,  starch  granules ;  2,  a  small  air  bubble  and  i)art  of  a  large  one  ;  3,  yeast  torulaj ;  4,  a 
mould  (Aspergillus  glaucus) ;  5,  linen  fibres  ;  0,  cotton  fibres  ;  7,  wool ;  8,  hair, 
human  ;  9,  epithelium  scales  ;  10,  micrococci ;  11,  bacilli  and  spores  (B.  subtilis). 
Magnified  about  250  diameters. 


MICROSCOPICAL  EXAMINATION  OF  COMMON  OBJECTS.     27 

coiisidenihly  in  size  ;  iiiuler  tlie  liii,'h  ])()\ver  they  are  clear,  flat,  ovoid 
particles  (lig.  29,  1),  with  a  sharp  outline  when  exactly  focussed.  Notice 
the  chanije  in  appearance  of  the  outline  as  the  microscope  is  focus-sed  up 
and  down.  On  close  examination  fine  concentric  lines  are  to  be  seen  in  the 
granules  arranged  around  a  minute  s])ot  which  is  generally  placed  eccen- 
trically near  the  smaller  end  of  the  gianule.  Sketch  two  or  three  starch 
granules. 

Notice  the  appearance  of  air-bubble.s  in  the  water.  If  comparatively 
large  they  are  clear  in  the  middle,  with  a  broad  dark  border  due  to 
refraction  of  the  light  ;  if  small  they  may  look  entii'ely  dark. 

2.  Examine  some  yeast  which  has  been  grown  in  solution  of  sugar. 
Observe  the  yeast-particles  or  torulw,  some  of  them  budding.  Each  torula 
contains  a  clear  vacuole,  ami  has  a  well-defined  outline,  due  to  a  membrane. 
Sketch  two  or  three  toruhe. 

3.  Examine  some  mould  in  water.  Notice  the  long  branching  filaments 
(hyphiv),  and  also  the  torula-like  particles  (spores)  from  which  hyphse  may  in 
some  instances  be  seen  sprouting.     Sketch  part  of  a  hypha. 

4.  Examine  fibres  of  linen  and  of  cotton  in  water,  using  a  high  power. 
Compare  the  well-defined,  rounded,  relatively  straight  or  but  slightly 
twisted  linen,  with  the  longer,  broader  but  thinner,  and  more  twisted 
cotton  fibres.     Sketch  one  of  each  kind. 

5.  Mount  one  or  two  hairs  from  the  head  in  water  and  look  at  them  first 
with  the  low,  then  with  the  high  power.  Examine  also  fibres  from  any 
woollen  material  and  compare  them  with  the  hairs.  They  have  the  same 
structure,  although  the  wool  is  finer  and  is  curled  ;  its  structure  may  be 
obscured  by  the  dye.     Draw  one  or  two  of  each. 

6.  Examine  a  drop  of  hay  infusion,  which  has  been  standing  a  day  or  two, 
for  bacteria  and  other  putrefactive  organisms.  The  active  movements  which 
these  exhibit  are  due  to  minute  cilia  or  flagella,  which  can  only  be  made 
.visible  by  special  staining  methods  and  a  very  high  magnifying  power.  Any 
minute  inactive  particles,  organic  or  inorganic,  which  occur  in  this  or  other 
fluids  may  be  seen  to  exhibit  a  peculiar  tremulous  dancing  movement  which 
is  known  as  the  'Brownian'  movement. 

7.  Examine  some  dust  of  the  room  in  water  with  a  high  power.  In 
addition  to  groups  of  black  particles  of  carbon  (soot)  there  will  probably 
be  seen  fibres  of  linen,  cotton,  or  wool,  and  shed  epithelium-cells  derived 
from  the  epidermis. 


28  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSONS  II.  AND  III. 
STUDY  OF  THE  HUMAN  BLOOD-CORPUSCLES. 

1.  Having  cleaned  a  slide  and  cover-glass,  prick  the  finger  above  the  nail 
and  mount  a  small  drop  of  blood  quickly,  so  that  it  has  time  neither  to  dry 
nor  to  coagulate.     Examine  it  at  once  with  the  higli  jjower. 

Note  {a)  the  coloured  corpuscles  mostly  in  rouleaux  and  clumps,  but  some 
lying  apart  seen  flat  or  in  profile  ;  (6)  the  colourless  corpuscles,  easily  made 
out  if  the  cover-glass  is  touched  by  a  needle,  on  account  of  their  tendency  to 
stick  to  the  glass,  whilst  the  coloured  corpuscles  are  driven  past  by  the 
currents  set  up  ;  (c)  in  the  clear  spaces,  fibrin-filaments  and  elementary 
particles  or  blood-platelets. 

Sketch  a  roll  of  coloured  corpuscles  and  one  or  two  colourless  corpuscles. 
Count  the  number  of  colourless  corpuscles  in  a  field  of  the  microscope. 

2.  To  be  made  as  in  §  1 ,  but  the  drop  of  blood  is  to  be  mixed  upon  the  slide 
with  an  equal  amount  of  isotonic  saline  solution,  so  that  the  red  corpuscles 
tend  to  be  less  massed  together,  and  their  peculiar  shape  is  better  displayed. 

Sketch  a  red  corpuscle  seen  on  the  flat  and  another  in  profile  or  (optical 
section).     Also  a  crenated  corpuscle. 

Measure  ten  red  corpuscles,  and  from  the  results  ascertain  the  average 
diameter  of  a  corpuscle.  Measure  also  the  largest  and  the  smallest  you  can 
find. 

3.  Make  a  preparation  of  blood  as  in  §  1  and  put  it  aside  to  coagulate* 
Keep  the  edges  from  drying  by  placing  it  in  a  moist  chamber  or  by  occasion- 
ally breathing  upon  it.  After  a  few  minutes  place  a  drop  of  1  p.c.  methyl 
violet  at  one  edge  of  the  cover  and  allow  this  to  pass  in  and  mix  with  the 
blood  :  it  may  be  drawn  through  the  preparation  by  applying  a  small  piece 
of  blotting  paper  to  the  opposite  edge.  The  dye  stains  the  nuclei  of  the 
white  corpuscles,  the  blood-platelets,  the  network  of  fibrin-filaments,  and 
the  membranes  of  the  red  blood-corpuscles. 

The  three  preparations  just  described  cannot  be  kept,  but  the  two  follow- 
ing will  serve  as  permanent  preparations  of  blood  : — ■ 

4.  To  fix  and  stain  the  coloured  corpuscles  : — Place  upon  a  slide  a  drop  of 
1  p.c.  osmic  acid  mixed  with  an  equal  amount  of  saturated  aqueous  solution 
of  eosin.  Prick  the  finger,  and  mix  the  blood  directly  with  the  coloured 
fluid,  stirring  them  together  with  a  needle.  Cover  the  mixture  and  put 
aside  for  an  hour,  protected  from  evaporation  ;  then  place  a  drop  of  glycerine 
and  water  at  the  edge  of  the  cover-glass.  When  this  has  passed  under  fix 
the  cover-glass  with  gold  size. 

5.  To  study  the  granules  of  the  colourless  corpuscles  and  their  different 
reactions  to  staining  reagents,  a  film  of  blood  is  inclosed  between  two  cover- 
glasses,  which  are  at  once  separated  and  the  film  on  each  quickly  dried  in  the 
air.  A  slide  may  be  used  instead  of  a  cover-glass  ;  the  drop  of  blood  is  placed 
close  to  the  ground  edge  of  one  slide  and  this  is  drawn  evenly  over  the 
middle  of  another.  The  films  are  fixed  by  immersion  for  one  hour  or  more 
in  a  mixture  of  alcohol  and  ether,  equal  parts  of  each.  They  are  then  stained 
by  (1)  a  saturated  solution  of  eosin  in  75  p.c.  alcohol  (three  minutes),  after 
which  they  are  rinsed  with  water,  and  are  then  treated  with  (2)  a  1  p.c. 


sTri>Y  OF  riiK  Hr:vrAN  hi.ood-c^orpuscles. 


29 


Fig.  30. — H-EMacytomkikk  si, mi:,  ullku  in  stiUAKKs  for  the  knumkiiation 

OK   BLOOD-CORPUSCLES. 


Fig.  31.— Oliver's  apparatus  for  estimating  the  number  of  corpuscles 
in  blood  by  means  of  the  opacity  method. 

a  pipette  for  measuring  blood ;  b,  dropper  for  adding  mixing  solution  ;  c,  graduated 
'  tube  ;  d,  mode  of  observing. 

a,  b,  c,  natural  size. 


30  THE   ESSENTIALS  OF  HISTOLOGY. 

solution  of  metliylene  blue  (one  minute).     The  film   is  again  rinsed  with 
water,  rapidly  dried,  and  mounted  in  xylol  balsam  or  dammar.^ 

6.  Mount  in  xylol  balsam  or  dammar  sections  of  marrow  from  a  long 
bone  of  a  rabbit  fixed  with  mercuric  chloride  or  forniol  and  stained  with 
eosni  and  methylene  blue.  Observe  the  fat-cells,  the  supporting  reticular 
tissue,  the  proper  marrow-cells  in  this  ti.ssue,  the  myeloplaxes  and  the 
erythroblasts. 

7.  Tease  in  salt  solution  or  serum  some  of  the  red  marrow  from  the  rib  of 
a  recently  killed  animal.  Observe  and  sketch  the  proper  marrow  cells  and 
look  for  myeloplaxes  and  nucleated  coloured  blood-corpuscles  (erythroblasts). 

8.  Make  a  film  preparation  of  red  marrow  by  smearing  a  little  upon  a 
cover-glass  or  slide,  allowing  it  to  dry  quickly,  and  placing  it  in  a  mixture  of 
equal  parts  of  ether  and  alcohol.  After  an  hour  or  more  in  this,  the  prepara- 
tion may  be  stained  with  eosin  and  methylene  blue  in  exactly  the  same  way 
as  a  film  preparation  of  blood  (see  §  5),  and  mounted  in  xylol  balsam  or 
dammar. 

9.  Enumeration  of  the  blood-corpuscles.  This  is  done  by  some  form  of 
blood-counter  such  as  the  hsemacytometer  of  Gowers,  or  the  similar  apparatus 
of  Thoma.  This  instrument  consists  of  a  glass  slide  (fig.  30),  the  centre  of 
which  is  ruled  into  ^^  millimeter  squares  and  surrounded  by  a  glass  ring 
j\j  mm.  thick  (in  Gowers'  instrument,  the  ruling  is  into  i  mm.  squares  with 
a  ring  I  mm.  thick).  There  must  also  be  provided  a  pipette  (fig.  31,  a)  for 
measuring  the  blood,  constructed  to  hold  about  .5  cubic  millimeters  of  fluid  ;  a 
dropper  (fig.  31,  b)  to  deliver  the  diluting  solution;  a  small  cylindrical  mixing- 
glass,  not  shown  in  the  figure,  with  a  mark  indicating  100  times  the  capacity  of 
the  blood  pipette  ;  a  small  glass  stirrer,  and  a  guarded  needle.  The  diluting 
solution  may  either  be  that  of  Hayem,  viz.  distilled  water  200  cc,  sulphate 
of  soda  5  grms.,  common  salt  1  grra.,  corrosive  sublimate  0'5  grm.,  or  that  of 
Mai'cano,  viz.  97  cc.  of  a  solution  of  sulphate  of  soda  in  distilled  water  of  sp. 
gr.  1020,  to  which  is  added  chloride  of  .sodium  1  grm.,  and  formol  3  cc. 
A  little  of  the  diluting  solution  is  put  in  the  mixing  vessel,  the  finger  is 
pricked,  and  the  pipette  filled  exactly  with  blood  (by  capillarity).  The  blood 
is  then  washed  out  of  it  with  diluting  solution,  by  aid  of  the  dropper,  into  the 
mixing  vessel,  which  is  now  filled  up  to  the  100  mark  with  diluting  solution, 
and  the  blood  and  this  are  thoroughly  mixed.  A  drop  of  the  mixture  is  next 
placed  in  the  centre  of  the  cell,  the  cover-glass  is  gently  laid  on  (so  as  to 
touch  the  drop,  which  thus  forms  a  layer  ^'^y  mm.  thick  between  the  slide 
and  cover-glass),  and  pressed  down  by  two  brass  springs.  In  a  few  minutes 
the  corpuscles  have  sunk  to  the  bottom  of  the  layer  of  fluid  and  rest  on  the 
squares.  The  number  in  ten  squares  is  then  counted,  and  this,  multiplied 
by  100,  gives  the  number  in  a  cubic  millimeter  of  the  mixture,  or  if  again 
multiplied  by  100  (the  amount  of  dilution)  the  number  in  a  cubic  millimeter 
of  blood. 

For  the  enumeration  of  the  white  corpuscles  the  blood  is  diluted  only  10 
times  instead  of  100  times.  It  is  also  convenient  to  use  one  half  per  cent, 
solution  of  acetic  acid  just  coloured  with  methyl  violet  as  a  diluent  (Thoma). 
This  destroys  the  coloured  corpuscles  and  stains  the  nuclei  of  the  white. 

A  rapid  method  of  estimating  the  number  of  colouVed  corpuscles  is  that 
devised  bj'  G.  Oliver.  The  blood  is  taken  up  as  before  in  a  capillary  pipette 
(fig.  31,  «),  and  is  washed  out  of  this  with  Hayem's  fluid  by  the  dropper,  b, 
into  a  flattened  graduated  glass  mixer,  c,  the  diluent  being  added  until  the 
flame  of  a  small  wax  candle  in  a  dark  room  will  just  show  sharply  through 
the  mixture,  when  the  vessel  is  held  close  to  the  eye  and  about  ten  feet  from 
the  candle  and  so  that  the  light  traverses  the  greater  thickness  of  fluid.    The 

^  Other  stains,  such  as  Elu'lich's  tri-aoid  and  the  Ehrlich-Biondi,  may  also  be 
employed  for  films. 


STUDY   OF  THE   HUMAN   BLOOD-CORPUSCLES.  31 

graduations  are  so  arranged  that  for  noinial  blood  (5,000,000  corpuscles  per 
cub.  mm.),  the  mixture  will  now  stand  exactly  at  the  100  mark  :  if  the  blood 
contain  more  or  fewei-  corpuscles  than  normal,  it  will  re(iuire  a  greater  or 
less  dilution  to  attain  the  requisite  tianslucejicy,  and  the  mark  at  which  the 
mixture  then  stands  will  indicate  the  percentage  of  corpuscles  as  compared 
with  the  normal. 

Another  rapid  method  of  estimating  the  relative  number  of  blood-cor- 
puscles is  to  (ieternnne  the  corpuscular  volume  in  a  known  amount  of  blood. 
This  is  done  by  the  use  of  the  lucmatocrit,  in  which  the  blood,  suitably 
diluted,  is  centrifugalised  and  the  volume  of  corpuscles  read  off  on  a  scale. 


The  coloured  blood-corpuscles. — The  coloured  corpuscles  are  com- 
posed of  a  delicate  colourless  highly  elastic  (1  protoplasmic)  envelojye, 
and  coloured  Jluid  contents,  consisting  mainly  of  a  solution  of  haemoglobin. 


Fig.  32.— Human  red  blood-corpuscles  :  Photograph  magnified  650  diameters. 

The  existence  of  such  an  envelope  is  shown  by  the  osmotic  effect  of 
water  upon  the  corpuscle,  which  passing  in  through  the  envelope, 
distends,  and  eventually  bursts  the  corpuscle  and  sets  free  the  con- 
tents. The  description  which  is  current  in  many  text-books  that 
the  red  corpuscles  consist  of  a  porous  solid  stroma,  permeated  with 
dissolved  haemoglobin,  is  incompatible  with  this  and  similar  reactions. 
Moreover,  the  envelope  can  be  distinctly  seen  with  the  microscope, 
especially  in  the  amphibian  corpuscle,  and  can  be  stained  by  reagents. 
The  envelope  contains  lecithin  and  cholesterin  in  considerable  amount, 
and  these  substances  impart  a  certain  greasiness  to  the  surface  of 
the  corpuscle.     It  is  in  all  probability  due  to  such  greasiness  that 


32  THE   ESSENTIALS   OF   HISTOLOGY. 

the  corpuscles  run  together  into  rouleaux  when  the  blood  comes  to 
rest  (see  p.  43). 

Under  the  microscope  blood  is  seen  to  consist  of  a  clear  fluid 
{plasma),  in  which  are  suspended  the  blood -corjmsdes  (fig.  32).  The 
latter  are  of  two  kinds  :  the  red  or  coloured  (erythrocytes),  which  are 
by  far  the  most  numerous,  and  the  white,  pale,  or  colourless  {leucocytes). 
In  addition  to  these  more  obvious  corpuscles,  blood  contains  a 
variable  number  of  minute  particles  which  were  termed  by  Zimmer- 
mann  the  elementary  particles  of  the  blood,  but  which  are  now  more 
usually  known  as  the  hlood-ptlatelets  on  account  of  their  flattened  form. 

Erythrocytes. — When  seen  singly  the  coloured  corpuscles  are  not 
distinctly  red,  but  appear  of  a  reddish-yellow  tinge.  In  the  blood 
of  man  and  of  all  other  mammals,  except  the  Camelidiie,  they  are 
biconcave  circular  disks.  Their  central  part  usually  has  a  lightly 
shaded  aspect  under  a  moderately  high  po\ver,  but  this  is  due  to  their 
biconcave  shape,  not  to  the  presence  of  a  nucleus.  They  have,  as  just 
stated,  a  strong  tendency  to  become  aggregated  into  rouleaux  and 
clumps  when  the  blood  is  at  re.st,  but  if  it  is  disturbed  they  readily 
become  separated. 

If  the  density  of  the  plasma  is  increased  in  any  way,  as  by  evapora- 
tion, many  of  the  red  corpuscles  become  shrunken  and  crenated  by 
the  passage  of  water  out  of  the  corpuscle.  On  the  other  hand,  a 
diminution  in  the  density  of  the  plasma  tends  to  cause  the  red 
corpuscles  to  become  cup-shaped,  but  it  is  erroneous  to  describe  this  as 
the  normal  form  of  the  corpuscle. 

The  average  diameter  of  the  human  red  corpuscle  is  0"0075  milli- 
meter^ (about  ■3-i>Vo  inch),  but  a  few  will  always  be  found  somewhat 
larger  (0-0085)  and  a  few  somewhat  smaller  (0'0065  mm.).- 

There  are  from  four  to  five  millions  of  coloured  corpuscles  in  a 
cubic  millimeter  of  blood. 

Leucocytes. — The  colourless  corpuscles  of  human  blood  are  proto- 
plasmic cells,  averaging  O'Ol  mm.  (^^oo  i"ch)  in  diameter  when 
spheroidal,  but  they  vary  much  in  size.  The}^  are  far  fewer  than 
the  coloured  corpuscles,  usually  numbering  not  more  than  eight  to 
ten  thousand  in  a  cubic  millimeter  (about  1  to  600  red  corpuscles). 
Moreover,  they  are  specifically  lighter,  and  tend  to  come  to  the 
surface  of  the  preparation.  If  examined  immediately  the  blood  is 
drawn,  they  are  spherical  in   shape,   but  soon  become  flattened  and 

^Also  expi-essed  as  7 "5  fx  or  micromillinieters  ;  a  micromillimeter  being  yJ^jj 
millimeter. 

'-  The  following  list  gives  the  diameter  in  parts  of  a  millimeter  of  the  red  blood- 
corpuscles  of  some  of  the  common  domestic  animals: — Dog,  0'0073;  rabbit, 
0-0069  ;  cat,  0-0065  ;  goat,  0-0041. 


LEUCOCYTES. 


33 


then  irregular  in  form  (fig.  33),  and  their  outline  continually  alters, 
owing  to  the  amoeba-like  changes  to  which  they  are  subject.  In  some 
kinds  {phagocytes)  the  protoplasm  tends  to  take  in  foreign  particles  with 
which  the  cells  come  in  contact ;  in  others  there  seems  to  be  little  or  no 
such  tendency.  Some  of  the  colourless  corpuscles  are  very  pale  and 
filled  with  fine  granules,  others  contain  coarser  and  more  distinct 
granules  in  their  protoplasm  ;  others  again  have  a  hyaline  protoplasm 
without  any  apparent  granules.  In  some  corpuscles  {lymphocytes) 
the  protoplasm  forms  only  a  relatively  thin  coating  to  the  nucleus. 
The  corpuscles  are  classified  according  to  the  character  and  appearance 
of  the  nucleus  and  the  nature  and  staining  qualities  of  the  granules  in 


Fig.   33. — Three  .vmceboid    white    corpuscles    of    the    newt,   killed    by 
instant.vneous  application  of  steam. 

a,  eosinophil  cell ;  h,  c,  polymorphous  cells.     The  nuclei  appear  multiple,  but  are  seen  to 
be  connected  with  fine  filaments  of  niiclear  substance  traversing  the  protoplasm. 

the  protoplasm.  Thus  some  granules  are  readily  stained  by  basic  dyes 
such  as  methylene  blue,  and  such  granules  are  accordingly  termed 
basophil.  Distinct  coarse  basophil  granules  are,  however,  rare  in 
normal  blood,  although  cells  with  these  granules  are  normally  present 
in  the  marrow  and  in  some  connective  tissues,  and  make  their  appear- 
ance in  the  blood  in  leucocythsemia.  On  the  other  hand,  some 
granules  more  readily  take  up  colour  from  acid  dyes,  such  as  eosin, 
and  these  have  been  termed  oxi/phil  or  eosmophil.  Other  cells  possess 
granules  (amphophd)  which  are  stained  by  both  acid  and  basic  dyes  ;  and 
others  chiefly  by  neutral  dyes  {neutrophil).  In  some  cells  more  than 
one  kind  of  granule  is  met  with.  The  protoplasm  may  also  contain 
clear  spaces  or  vacuoles.  Each  leucocyte  has  at  least  one  nucleus, 
which  is  difficult  to  see  in  a  fresh  preparation,  but  is  easily  seen 
after  the  action  of  most  reagents  and  after  staining.  There  is  also  a 
centrosome  with  attraction-sphere,  but  special  methods  of  staining  are 
necessary  to  exhibit  these.     (See  fig.  9,  p.  7.) 

The  following  are  the  chief  varieties  of  leucocytes  : — 1.  Polymorphs. 
Cells  with  lobed  or  multipartite  nuclei  and  a  relatively  large  amount  of 
protoplasm,  which  is  highly  amoeboid  (fig.  33,  h  and  r).  These  are  often 
termed  multi-(poly-)nuclear,  but  the  nucleus  is  rarely  if  ever  multiple, 


34  THE   ESSENTIALS   OF   HISTOL(XtY. 

its  several  parts  being  nearly  always  joined  by  threads  of  nuclear 
substance.  The  cells  in  question  vary  in  size,  but  when  spherical  are 
usually  not  quite  0"01  mm.  in  diameter.  Their  protoplasm  stains 
with  eosin,  this  being  due  to  the  presence  of  fine  oxyphil  granules 
(Kanthack  and  Hardy).  They  are  highly  amoeboid  and  phagocytic, 
and  constitute  from  sixty  to  seventy  per  cent,  of  all  the  leucocytes 
of  the  blood  (&g.  .34,  a). 


Fig.  34. — Variou.s  kixds  of  colourle.ss  corpcscle.s,  showing  the  different 
CHAR.vcTERS  OF  THE  GRANULES.  ( From  a  film  preparation  of  normal  human 
blood.)     Two  of  each  kind  are  represented. 

2.  LymphocyteH. — These  are  small  cells,  with  a  very  limited 
amount  of  clear  protoplasm  around  the  nucleus,  which  is  simple, 
not  lobed  or  divided  (fig.  34,  hj.  The  amoiboid  phenomena  are 
less  marked  in  them  than  in  the  other  varieties  of  leucocytes. 
The  protoplasm  stains  with  methylene  blue.  They  are  about  0*0065 
mm.  in  diameter,  but  some  are  larger  and  appear  to  be  transitional 
between  this  and  the  next  variety.  They  constitute  from  fifteen  to 
thirty  per  cent,  of  the  total  number  of  leucocytes  in  the  blood.  They 
are  relatively  more  numerous  in  infancy. 

3.  Macrocyfes. — Large  uninucleated  cells  similar  to  the  last,  but 
larger,  and  containing  much  more  protopla-^im  (fig.  34,  c).  Some, 
however,  are  smaller  and  are  regarded  as  transitional  forms  from  the 
last  variety.  The  nucleus  may  be  spherical,  oval,  or  kidney-shaped. 
The  protoplasm  is  hyaline  :  it  stains  slightly  with  methylene  blue, 
perhaps  owing  to  very  fine  basophil  granules.  These  cells  are  highly 
amoeboid  and  phagocytic.  Including  the  transitional  forms,  they 
constitute  about  five  per  cent,  of  all  the  leucocytes  in  blood. 

4.  Eosinophils. — These  are  characterised  by  their  coarse  granules, 
which  stain  deeply  with  acid   dyes,   such   as   eosin.      Their  average 


LEUCOCYTES. 


35 


diameter  in  the  spherical  condition  is  UOl  mm.  The  nucleus  may  be 
simple  or  lobed  (fig.  34,  d ;  fig.  33,  a).  They  are  ameboid,  but  less 
actively  so  than  the  finely  granular  cells.  They  are  more  variable  in 
number  than  the  other  varieties,  constituting  sometimes  not  more  than 
one  per  cent.,  and  at  other  times  as  much  as  ten  per  cent,  of  the 
total  leucocytes  of  blood. 

5.  Baiiophih. — These  are  rarely  if  ever  found  in  normal  blood  (adult), 
but  occur  in  children  and  in  certain  pathological  conditions  affecting 
the  bone  marrow. 

Blood-platelets. — In  the  clear  fiuid  in  which  the  blood-corpuscles  are 
suspended,  a  network  of  fine  straight   intercrossing  filaments  (fibrin) 


Fig.  35.— Network  ok    fibrin,    shown 

AFTKR  W.^SHINCt  AW.\Y  THE  CORPUSCLES 
FROM  A  PREFAR.\TION  OF  BLOOD  THAT 
HAS  BEEN  ALLOWED  TO  CLOT  ;  MANY  OF 
THE  FILAMENTS  RADIATE  FROM  SMALL 
CLUMPS  OF  BLOOD-PL.\TELETS. 


Fig.  36. — Blood-corpuscles  and  elemen- 
tary   PARTICLES    OR    BLOOD-PLATELETS, 

WITHIN  A  SMALL  VEIN.     (From  Osier.) 


ACi-^v?^;;^,  Fig.    .38. — Blood-pl.4TELets,    highly 

magnified,  showing  the  amceboid 
forms  which  they  assume  when 
examined  under  suitable  condi- 
tions, and  also  exhibiting  the 
chromatic  particle  which  each 
platelet  contains,  and  which  has 

BEEN  REGARDED  AS  A  NUCLEUS.    (After 

Fig.  37. — A  mass  of  blood-platelets,  Kopsch.) 

FROM  HUMAN  BLOOD.  (Osier.) 
A  few  at  the  edge  ai-c  detached  from  the  rest. 
The  preparation  had  been  kept  in  salt  solu- 
tion on  the  warm  stage  for  some  time,  thus 
causing  a  partial  breaking  up  of  the  mass  of 
platelets.  These  will  be  observed  to  have 
filaments  attached  to  them. 

soon  makes  its  appearance  (fig.  35).  These  often  seem  to  radiate  from 
minute  round  colourless  discoid  particles  less  than  one-third  the  diameter 
of  a  red  corpuscle,  either  separate  or  collected  into  groups  or  masses, 
of  variable,  sometimes  of  considerable,  size.  These  are  the  elementary 
particles,  blood-platelets,  or  thrombocytes.     In  the  blood-vessels  they  are 


36  THE   ESSENTIALS   OF   HISTOLOGY. 

discrete  but  immediately  clump  together  in  drawn  blood  (fig.  37). 
If,  however,  the  blood  is  examined  on  agar  jelly  containing  certain  salts 
in  definite  proportions,  the  platelets  can  be  kept  separate,  and  may 
then  be  submitted  to  very  high  powers  of  the  microscope.  The  result 
of  such  examination  seems  to  show  that  the  blood-platelets  are  not 
mere  inert  particles,  as  has  generally  been  supposed,  but  that  they  are 
protoplasmic  and  amoeboid,  and  that  each  one  contains  a  nucleus 
(fig.  38),  that  they  are  in  fact  minute  cells  (Deetjen).  Blood  platelets 
vary  greatly  in  number :  they  are  estimated  by  Brodie  and  Russell  to 
amount  to  from  5  millions  to  45  millions  in  the  cubic  centimeter  of  blood. 
Fatty  particles,  derived  from  the  chyle,  may  also  occur  in  the 
plasma. 


0^    ^-  V<^>,^^ 


V>  ft 


m: 


u. 


Fig.   39. — Development  of  blood-vessels  and   blood-corpuscles    in  the 
vascular  area  op  the  guinea-pig. 

hi,  blood-corpuscles  becoming  fi-ee  in  the  interior  of  a  nucleated  protoplasmic  mass. 

Development  of  red  blood-corpuscles. — In  the  embryo,  the  first-formed 
coloured  hlood-corpusdes  are  amoeboid  nucleated  cells,  the  protoplasm 
of  which  contains  haemoglobin.  These  embryonic  blood-corpuscles  are 
developed  within  cells  of  the  mesoderm  (mesenchyme),  which  are 
united  with  one  another  to  form  a  syncytium  (fig.  39).  The  nuclei 
of  the  cells  multiply,  and  around  some  of  them  there  occurs  an 
aggregation  of  coloured  protoplasm.  Finally  the  network  becomes 
hollowed  out  by  an  accumulation  of  fluid  in  the  syncytial  protoplasm, 
and  thus  are  produced  a  number  of  capillary  blood-vessels,  within 
which  the  coloured  nucleated  portions  of  protoplasm  are  set  free 
as  embryonic  blood-corpuscles  (eri/throblnsts,  fig.  39,  bl).  Within  the 
circulation  these  multiply  by  mitotic  division,  and  thus  become 
rapidly  more  numerous. 

In  later  embryonic  life,  nucleated  coloured  corpuscles  disappear  from 
mammalian  blood,  and  are  replaced  by  the  usual  discoid  corpuscles. 
Many  of  these  are  doubtless  derived   from    the  nucleated  embryonic 


DEVELOPMENT  OF   BLOOD-CORPUSCLES. 


37 


blood-cells,  the  absence  of  the  nucleus  being  accounted  for  either  by 
its  atrophy  or  extrusion  from  the  cell  or  l>y  the  separation  of  a  part 
of  the  coloured  cell-substance.  The  foetal  liver  has  been  supposed  to 
be  one  of  the  places  of  formation  of  red  blood-corpuscles.  Erythrocytes 
are  also  formed  at  a  somewhat  later  stage  of  development  within 
certain  cells  of  the  connective  tissue  (vafidformative  cells),  a  portion  of 
the  substance  of  the  cell  becoming  coloured  by  haemoglobin,  and 
separated  into  globular  particles  (fig.  40,  a,  b,  c),  which  are  gradually 
moulded  into  disk-shaped  red  corpuscles.      In  the  meantime  the  cells 


Fig  40.— Blood-corpuscles  developing  within  connective-tissue  cells. 

a,  a  cell  containing  diffused  haemoglobin  ;  b,  a  cell  filled  with  coloured  globules  ;  c,  a  cell 
containing  coloured  globules  in  the  protoplasm,  within  which  also  are  numerous 
vacuoles  ;  d,  an  elongated  cell  with  a  cavitj'  in  its  protoplasm  occupied  by  fluid  and 
blood-corpuscles  mostly  globular ;  e,  a  hollow  cell,  the  nucleus  of  which  has  multi- 
plied. The  new  nuclei  are  arranged  around  the  wall  of  the  cavity,  the  corpuscles  in 
which  have  now  become  discoid  ;  /,  shows  the  mode  of  union  of  a  'haemapoietic'  cell, 
which  in  this  instance  contains  only  one  corpuscle,  with  the  prolongation  (bl)  of  a 
previously  existing  vessel. 

become  hollowed  out,  and  join  -with  similar  neighbouring  cells  to  form 

blood-vessels  (fig.  40,  d,  e,  f).     The  process  is  therefore  the  same  as  in 

the    early    embryo,    except   that  cell-nuclei   are  not  included  in    the 

hsemoglobin-holding   protoplasm. ^ 

^It  has  been  suggested  by  some  writers  that  the  vasoformative  cells  con- 
taining coloured  corpuscles  in  various  stages  of  formation  are  in  reality  portions 
of  an  already  formed  vascular  network  which  is  undergoing  atrophy ;  and 
that  the  corpuscles  within  such  cells  are  not  in  process  of  formation  but  of 
disappearance.  But  since  the  appearances  in  question  are  seen  in  parts  in  which 
vascular  tissues  (such  as  fat)  are  undergoing  not  atrophy  but  formation  ;  and  since, 
moreover,  the  h^matoidin  crystals  and  pigment  granules  which  are  character- 
istic of  the  disintegration  of  erythrocytes  within  cells  are  not  present,  it  seems 
more  reasonable  to  interpret  the  appearances  as  indicative  of  intracellular  de- 
velopment of  blood-corpuscles  by  differentiation  of  part  of  the  protoplasm  of  the 
vasoformative  mesenchyme  cell,  rather  than  a  degeneration  of  already  formed 
blood-vessels  and  blood-corpuscles. 


38  THE    ESSENTIALS   OF   HISTOLOGY. 

Formation  in  bone-marrow.— Although  no  nucleated  coloured  cor- 
puscles (erythroblasts)  are  as  a  rule  to  be  seen  in  the  blood  in  post- 
embryonic  life,  they  are  found  in  the  marrow  of  the  bones,  and 
in  some  animals  also  found  in  the  spleen.  They  vary  in  size,  most 
measuring  about  "007  mm.  (normoblasts),  but  some  being  considerably 
larger  (megaloblasts),  and  others  considerably  smaller  (microblasts). 
It  is  probable  that  the  red  disks  are  formed  from  these  nucleated  red 
corpuscles  of  the  marrow  by  the  nucleus  disappeaiing  and  the  coloured 

m'  I  ^  m!        e  m  to 

\  M       i  i  i 


mt'j  III  m     ^  ni   c" 

Fig  4L — Red  marbow  of  tocxg  BABBrr.     Magnified  450  diameters. 

e,  erythrocytes ;  e',  erythroblasts ;  t",  an  erythroblast  undergoing  mitotic  division  ;  /,  a 
polymorph  leucocyte ;  m.  ordinary  myelocytes ;  m\  myelocytes  undergoing  mitotic 
division ;  'o,  an  eosinophil  myelocyte ;  6,  a  basophil  myeloc5i^  ;  raeg,  a  giant-cell  or 
megakaryocyte. 

protoplasm  becoming  moulded  into  a  discoid  shape.     At  what  time  this 

formation  of  blood-corpuscles  in  the  bone-marrow  begins  has  not  been 

ascertained,  but  after  it  has  commenced  it  continues  throughout  the 

whole   of  life — the   red   marrow,   especially   that   of  the   ribs,  being 

especially   active   in   this    respect.      In    mammals    the   formation   of 

nucleated  coloured  corpuscles  appears  to  take  place  within  the  tissue 

of  the  marrow  external  to  the  blood-vessels.     It  is  uncertain  to  what 

extent  the  capillary  vessels  of  the  marrow  are  limited  by  a  complete 

endothelium   (see  p.  40),  but  in  any  case  the   formed  erythroblasts 

seem  to  readily  pass  into  the  blood  stream.^ 

^  In  birds  the  erythroblasts  are  coutined  to  the  large  blood-channels  of  the 
marrow,  and  the  transformation  into  erythrocytes  occurs  within  these  channels. 


MARROW   OF   BONE. 


39 


The  marrow  of  boiu'  is  of  a  yellow  colour  in  the  shafts  of  the  long 
bones  of  most  animals,  and  is  there  largely  composed  of  adipose 
tissue,  but  in  the  shafts  of  the  long  bones  of  some  animals,  and  in  the 
cancellated  tissue  of  most,  it  is  usually  red,  the  colour  being  partly 
due  to  the  large  amount  of  blood  in  its  vessels.  This  red  marrow 
(tig.  41)  is  chieriy  composed  of  spherical  cells — the  mijelocijtes  or 
marrow-cells — which  resemble  rather  large  blood-leucocytes,  and, 
like  these,  are  amoeboid.  They  also  exhibit  the  same  kind  of 
differences  as  to  the  character  of  the  granules  which  they  contain, 
some  being  oxyphil  and  others  amphophil  or  neutrophil.  But  while 
the  blood-leucocytes  rarely  contain  any  coarse  basophil  granules,  some 


k  I  m 


0        p 


^  Q  ^^  I  Si  C)  ;fXI  « 


Fig.  42. — Cklls  of  the  red  marrow  of  the  gdinea-pig.     (Highly  magnified.) 

a,  a  large  cell,  the  nucleus  of  which  apisears  to  be  partly  divided  into  three  by  constric- 
tions ;  h,  a  cell,  the  enlarged  nucleus  of  which  shows  an  appearance  of  being  con- 
stricted into  a  number  of  smaller  nuclei ;  c,  a  so-called  giant-cell  or  myeloplaxe  with 
many  nuclei ;  d,  a  smaller  myeloplaxe  with  three  nuclei ;  e-i,  proper  cells  of  the 
marrow  ;  j-t,  various  forms  of  coloured  nucleated  cells  (erythroblasts),  some  in 
process  of  division  ;  in  others  the  nucleus  appears  to  bo  undergoing  atrophy. 

of  the  marrow-cells  contain  these  in  considerable  numbers.  There 
are  also  to  be  seen  mingled  with  the  marrow-leucocytes  a  number  of 
corpuscles  somewhat  smaller  in  size,  nucleated,  and  at  least  some 
of  them  amoeboid,  but  of  a  reddish  tint  (fig.  41,  e').  These  cells,  which 
are  termed  erythroblasts,  resemble  the  nucleated  coloured  blood-corpuscles 
of  the  embryo,  and  are  believed  to  be  cells  from  which  the  coloured 
blood-disks  become  developed.  Many  of  them  are  in  process  of 
mitotic  division.  Others  are  seen  with  the  nucleus  in  a  more  or  less 
atrophied  condition  (fig.  42,  k) ;  from  this  it  may  perhaps  be  inferred 
that  the  transformation  into  a  discoid  blood-corpuscle  is  accompanied 
by  the  disappearance  of  the  nucleus  (Bizzozero).     Lastly,  the  marrow 


40  THE  ESSENTIALS  OF   HISTOLOGY. 

contains  a  number  of  very  large  cells,  the  giant-cells  or  myeloplaxes 
of  Robin  (fig.  41,  meg:  fig.  42,  a-d).  These  are  especially  numerous 
wherever  bone  is  becoming  absorbed,  but  are  not  confined  to  such 
situations,  being  indeed  normal  constituents  of  marrow.  Sometimes 
they  possess  several  nuclei,  but  most — the  so-called  megakari/oci/tes— 
contain  but  one  large  nucleus,  which  has  usually  an  annular  form. 
They  are  also  characterised  by  possessing  a  number  of  centrioles 
grouped  together  near  the  nucleus.  Lastly,  the  existence  of  cells 
within  the  marrow  containing  blood-corpuscles  in  various  stages  of 
transformation  into  pigment,  similar  to  those  which  occur  in  the 
spleen-pulp,  has  been  noted  (Osier). 

The  marrow  is  very  vascular,  the  capillaries  and  veins  being  large 
and  thin-walled;  indeed,  according  to  some  authorities,  the  walls  of 
the  capillaries  are  imperfect,  so  that  there  is  an  open  communication 
between  them  and  the  interstices  of  the  tissue,  and  in  this  way  it  is 
supposed  that  the  coloured  blood-disks,  which  are,  it  is  believed, 
produced  from  the  coloured  nucleated  cells  (erythroblasts)  of  the 
marrow,  may  get  into  the  circulation.  There  is  not,  however,  an 
interstitial  circulation  of  blood  in  the  marrow  such  as  is  found  in  the 
spleen,  nor  does  injection  material  such  as  carmine  gelatine  pass 
into  the  interspaces  of  the  tissue,  but  remains  confined  to  the  vessels, 
so  that  the  existence  of  an  open  communication  is  doubtful. 

Development  of  white  corpuscles. — ^The  ivhite  blood-  and  lymph- 
corpuscles  occur  originally  as  free  cells,  Avhich  are  believed  to  find 
their  way  into  the  vessels  from  the  circumjacent  mesoderm.  They 
do  not  occur  within  the  first-formed  blood-vessels  of  the  embryo  nor 
within  the  vasoformative  cells.  In  later  stages  of  fcetal  life  and 
during  the  whole  of  post-embryonic  life  they  become  formed  in  the 
bone-marrow  as  well  as  in  lymph-glands  and  other  organs  composed 
of  lymphoid  tissue,  and  pass  from  these  directly  into  the  lymphatics 
and  into  the  blood. 

It  is  probable,  but  has  not  been  ascertained  with  certainty,  that  the 
lymphocytes  are  all  produced  in  lymph-glands  and  other  lymphoid 
tissues,  and  that  the  macrocytes  are  formed  by  enlargement  of  the 
lymphocytes.  On  the  other  hand,  the  polymorphs  and  the  coarsely 
granular  oxyphil  cells  are  believed  to  be  formed  within  the  bone 
marrow,  which  contains  cells  of  similar  character.  Cells  with  well- 
marked  basophil  granules  are  also  met  with  in  bone  marrow,  and 
sometimes,  in  abnormal  conditions,  pass  in  large  numbers  into  the 
blood. 


HUMAN   BLOOD-CORPUSCLES.  41 


LESSON   IV. 

ACTION  OF  REAGENTS    UPON  THE  HUMAN  BLOOD- 
CORPUSCLES. 

1.  Make  a  preparation  of  luunan  blood,  and  apply  a  drop  of  water,  at  one 
edge  of  the  cover-glass.  Examine  at  a  place  where  the  two  fluids  are 
becoming  mixed.  Notice  particularly  the  first  effect  of  water  upon  both  red 
and  white  corpuscles,  as  well  as  the  ultimate  action. 

Sketch  both  kinds  of  corpuscles  under  the  action  of  water. 

2.  Repeat  on  another  preparation,  using  very  dilute  alkali  (0'2  per  cent, 
caustic  potash)  instead  of  water.  Notice  the  complete  solution  first  of  the 
white  and  then  of  the  coloured  corpuscles  as  the  alkali  reaches  them. 

3.  Repeat  on  another  preparation,  using  dilute  acetic  acid  (1  per  cent.). 
Observe  that  the  effect  of  the  acid  upon  the  coloured  corpuscles  is  similar 
to  that  of  water,  but  that  it  has  a  different  action  upon  the  colourless 
corpuscles. 

Sketch  two  or  three  of  the  latter  after  the  action  is  completed. 

4.  Make  a  prepai'ation  of  blood  mixed  with  salt  solution,  as  in  Lesson  II.  2, 
and  investigate  the  action  of  tannic  acid  (1  part  tannic  acid  to  100  of  distilled 
water)  in  the  same  way. 

Sketch  two  or  three  coloured  corpuscles  after  the  action  is  complete. 

5.  Examine  blood-crystals  of  rat,  guinea-pig,  and  squirrel.  Preparations 
of  htemoglobin  crystals  cannot  be  kept  permanently. 

6.  Prepare  hoemin  by  heating  a  dry  smear  of  blood  on  a  slide  with  glacial 
acetic  acid.     The  crystals  of  hyemin  are  permanent. 


Structure  of  erythrocytes. — The  action  of  reagents  upon  the 
human  red  blood-corpuscles  shows  that,  although  to  all  appearance 
homogeneous,    they    in    reality    consist    of 

an  external  envelope  of  colourless  material        "        ''         <'  ''        <" 

which  forms  a  thin  film  inclosing  the  dis- 
solved colouring  matter  or  hcenioglobin.    Thus, 

when  water  reaches  the  corpuscles,  it  passes  yH  .^^ 

through  the  film  and   swells  the  corpuscle,       •'"^''  '  ''       • 

causing  it  to  become  globular ;    eventually  Fig.  43. 

the  film  is  burst  through,  and  the  colouring  «-f,  successive  effects  of  water  upon 

o    '  &  a  red   corpuscle  ;    /,    effect    of 

matter  escapes  into  the  serum.     The  addition       solution  of  salt;  V,  effect  of 

I  tannic  acid. 

of    hyperisotonic   solution    of    salt,    on   the 

other  hand,  by  increasing  the  density  of  the  fluid  in  which  the 
corpuscles  float,  causes  diffusion  of  water  out  of  the  corpuscle,  and 
consequent  shrinking  and  corrugation  of  the  surface,  the  crenated  form 


42  THE   ESSENTIALS  OF   HISTOLOGY. 

(fig.  43,/)  being  thereby  produced.  The  same  change  is  brought  about 
by  evaporation  of  water,  if  the  blood  is  exposed  to  air.  The  separation 
of  hcBmoglobin  from  the  corpuscle  can  be  effected  not  only  by  water  (fig. 
43,  a-e),  but  also  b}^  dilute  acids,  by  the  action  of  heat  (60°  C),  the 
freezing  and  thawing  of  blood,  the  action  of  ether  or  chloroform,  and  the 
passage  of  electric  shocks.  Bile  and  dilute  alkalies  rapidly  cause  the  red 
corpuscles  to  become  spherical  and  then  almost  instantly  effect  their 
complete  solution  (haemolysis).  The  mixing  of  blood  from  one  species 
of  animal  with  the  blood  or  serum  of  animals  of  other  species 
frequently  also   has   a   similar    effect.      In   this   case   the    haemolytic 


Fig.  44.— Blood  crystals,  magnified. 
1,  from  human  blood  ;  2,  from  the  guinea-pig ;  3,  squirrel ;  4,  hamster. 

action  is  exerted  by  some  constituent  (hsemolysin)  of  the  foreign 
blood,  which  is  special  for  each  species  and  against  which  the  "  host " 
can  render  itself  immune  if,  prior  to  any  large  quantity  of  the  foreign 
blood  or  serum  being  injected,  successive  small  injections  be  made ; 
an  "  antiha^molysin "  being  gradually  produced.  This  fact  is  not 
only  of  interest  as  bearing  upon  the  general  doctrine  of  immunity, 
but  also  serves  to  detect  the  source  of  a  given  sample  of  blood. 

Tannic  acid  produces  a  peculiar  effect  upon  the  red  corpuscles  (fig. 
43,  g) ;  the  haemoglobin  is  discharged  from  the  corpuscle,  but  is  im- 
mediately altered  and  precipitated,  remaining  adherent  to  the  envelope 
in  the  form  of  a  round  or  irregular  globule  of  a  brownish  tinge 
(hsematin  ?). 

Some  of  these  reactions  occur  by  a  process  of  osmosis  as  iu  the  case  of 
water,  but  in  others  a  solution  of  the  envelope  of  the  corpuscle  is  produced 


HUMAN   BLOOD-COEPUSCLES.  43 

by  the  reuneiit,  ami  the  luemo^lobin  is  thu.s  allowed  to  escape.  The  lilui  or 
envelope  is  probably  composed  of  protoplasm  contaiuin<,',  besides  iiucleo- 
proteids,  lecitiiin  and  cholesterin  (myelin),  and  these  are  substances  which 
possess  many  of  the  physical  properties  of  fats,  although  of  a  different 
chemical  composition.  If  we  assume  that  .such  fatty  substances  form  an 
external  film  to  the  corpuscle,  the  running  of  the  red  disks  into  rouleaux  can 
readily  be  explained,  since  it  has  been  shown  by  Norris  that  disks  of  any 
material,  e.g.  cork,  suspended  in  a  fluid,  tend  in  the  same  way  to  adhere  in 
rouleaux,  provided  their  surfaces  are  covered  with  a  layer  which  is  not 
wetted  by  the  fluid.  We  may  also  explain  on  the  .same  hypothesis  the  fact 
that  no  I'ent  is  ever  seen  in  the  envelopes  of  the  red  corpuscles  even  when 
they  appear  to  have  burst  after  imbibition  of  water,  for,  if  the  film  which 
represents  an  envelope  is  myelinic  in  nature,  any  rent  in  it  would  tend 
immeil lately  to  close  up  again  when  the  opposed  edges  come  in  contact. 

It  was  also  shown  by  Norris  that  droplets  of  fluid  encoiupassed  by  myelin 
have  a  tendency  to  assume  a  flattened  shape. 

^  -^  /  '^_ 


L'    1    -^      ^ 


"*##♦„  ••1^' 


Fig.  45.— H^min  crystals,  jiagnifiep.  Fig.  4G.— Hjijiatoidin  crystals. 

(Prejer.)  (Frey.) 

The  more  solid  part  of  the  red  corpuscle  is  often  termed  the  stroma.,  but 
this  name  rests  upon  an  entirely  false  conception  of  the  structure  of  the 
corpuscle.  In  adopting  the  name,  it  was  supposed  that  the  corpuscle  is 
formed  of  a  homogeneous  porous  material  (stroma — Rollett),  in  the  pores  of 
which  the  hfemoglobin  is  contained,  but  there  is  no  reasonable  foundation 
for  this  belief,  which  fails  to  explain,  except  on  the  assumption  of  a  still  more 
complex  hypothesis,  the  well-known  osmotic  phenomena  of  the  corpuscle  ; 
whereas  the  supposition  that  there  exists  a  delicate  external  film  or  envelope 
inclosing  a  coloured  fluid  is  in  accordance  with  all  the  known  facts  regarding 
the  action  of  reagents  u])on  these  bodies.  It  is  true  that  in  the  fresh 
mammalian  corpuscle  the  envelope  is  too  delicate  to  be  actually  observed  in 
the  optical  section  of  the  corpuscle,  but  in  the  blood-corpuscles  of  amphibia 
it  can  be  quite  distinctly  seen,  and  with  any  slight  increase  in  density  of  the 
plasma  it  tends  to  become  wrinkled  and  the  creases  in  it  are  plainly  visible. 
In  these  corpuscles  also  the  nucleus  becomes  readily  displaced  in  drawn 
blood  from  its  position  in  the  centre  of  the  corpuscle  and  may  lie  quite  at 
the  side  ;  this  is  a  clear  indication  of  the  fluid  nature  of  the  contents  of  the 
corpuscle,  and  by  analogy  we  may  fairly  assume  a  similar  constitution  for 
the  mammalian  corpuscle.  Lastly,  it  is  possible  to  stain  the  envelope  of  the 
red  corpuscles  of  a  ditterent  colour  from  the  remainder  of  the  corpuscle. 

Blood-crystals — Haemoglobin. — In  the  blood  of  many  animals  (fig.  44), 
crystals   of    haemoglobin   readily    form   after   its    separation    from    the   red 


44  THE   ESSENTIALS   OF   HISTOLOGY. 

corpuscles.  These  crystals  are  rhombic  prisms  in  man  and  most  animals, 
e.g.  the  rat,  but  tetrahedra  in  the  guinea-pig,  and  hexagonal  plates  in 
the  squirrel.  In  these  animals  they  at  once  appear  on  shaking  up  the 
blood  with  chloroform  or  ether,  or  even  on  the  addition  of  water,  with  or 
without  subsequent  evaporation. 

Hsemin. — This  name  has  been  applied  to  the  minute  dark-brown  rhombic 
crystals  of  hydrochlorate  of  hsematin  (fig.  45),  which  are  formed  when  dried 
blnod  from  any  source  whatever  is  heated  with  glacial  acetic  acid. 

Haematoidin. — This  occui's  in  the  form  of  brownish  yellow  crystals  (fig.  46). 
It  is  found  in  old  blood  extravasations  and  in  other  places  where  blood- 
corpuscles  are  undergoing  disintegi-ation  within  the  tissues. 

Action  of  reagents  on  leucocytes. — The  structure  of  the  colourless 
corpuscles  is  also  brought  out  by  the  action  of  some  of  the  reagents 
above  noticed.  As  the  water  reaches  them  their  amceboid  movements 
cease ;   they  become  swollen  out  into  a  globular  form  by  imbibition 


Fig.  47. 

1,  first  effect  of  the  action  of  water  upon  a  white  blood-corpuscle  ;  2,  3,  white  corpuscles 
treated  with  dilute  acetic  acid  ;  v,  nucleus. 

of  fluid  (fig.  47,  1),  and  the  granules  within  the  protoplasm  can  be 
seen  to  be  in  active  Brownian  motion.  Their  nuclei  also  become 
clear  and  globular,  and  are  more  conspicuous  than  before.  With 
the  further  action  of  the  water,  the  corpuscle  bursts  and  the  granules 
are  set  free. 

Acids  have  an  entirely  different  action  upon  the  white  corpuscles. 
Their  nuclei  become  somewhat  shrunken  and  very  distinct  (fig.  47, 
2  and  3),  and  a  granular  precipitate  is  formed  in  the  protoplasm 
around  the  nucleus.  At  the  same  time,  a  part  of  the  protoplasm 
generally  swells  out  so  as  to  form  a  clear  bleb-like  expansion  (an 
appearance  which  also  often  accompanies  the  death  of  the  corpuscle 
from  other  causes).  Dilute  caustic  alkalies  rapidly  cause  the  complete 
destruction  of  the  white  corpuscles. 


BLOOD-COllPUSCLES   OF   AMriilBlA.  45 


LESSON    V. 
THE  BLOOD-CORPUSCLES  OF  AMPHIBIA. 

1.  Obtain  a  drop  of  frog's,  toad's  or  newt's  blood,  and  mix  it  witli  a  very 
small  quantity  of  salt  solution  upon  a  slide.  Examine  with  the  high  power. 
Notice  the  shape  of  the  colonized  corpuscles  both  wheu  seen  flat  and  edge- 
ways, and  the  nucleus  within  each. 

Measure  ten  corpuscles  (long  and  short  diameters),  and  from  the  results 
obtain  the  average  dimensions  of  a  corpuscle. 

Notice  also  the  colourless  corpuscles,  smaller  than  the  reil,  but  larger  than 
the  pale  corpuscles  of  human  blood,  although  otherwise  generally  resembling 
these. 

Sketch  two  or  three  red  corpuscles  and  as  many  white. 

Be  careful  not  to  mistake  the  rouuded  liberated  nuclei  of  crushed  red 
corpuscles  for  pale  corpuscles. 

Enormous  cells  and  nuclei  belonging  to  the  cutaneous  glands  as  well  as 
the  granular  secretion  of  those  glands  may  be  present  in  this  preparation  if 
it  is  obtained  from  the  newt's  tail. 

2.  Apply  a  drop  of  water  to  the  edge  of  the  cover-glass  of  the  same 
preparation  and  notice  its  action  upon  the  corpuscles. 

Sketch  two  or  three  corpuscles  altered  b}'  the  action  of  the  water. 

3.  Mount  another  drop  of  blood,  and  apply  dilute  acetic  acid  (1  per  cent.) 
instead  of  water  at  the  edge  of  the  cover-glass.  Make  sketches  showing  the 
effect  of  the  acid  upon  both  red  and  white  corpuscles. 

4.  Examine  the  corpuscles  of  newt's  blood  which  has  been  allowed  to  flow 
into  boric  acid  solution  (2  per  cent.).  Notice  the  effect  produced  upon  the 
coloured  corpuscles.     Sketch  one  or  two. 

5.  Mount  drops  of  glycerine-jelly  containing  {a)  frog's  blood  and  {h)  bird's 
blood,  previously  fixed  by  Flemming's  solution  and  stained  with  picro- 
carmine. 

6.  Make  a  film  preparation  of  amphibian  or  avian  blood  as  described  on 
p.  28,  §  5. 

The  coloured  blood-corpuscles  of  amphibia  {fig.  48),  as  well  as 
of  nearly  all  vertebrates  below  mammals,  are  biconvex  elliptical  disks, 
considerably  larger  than  the  biconcave  circular  disks  of  mammals. ^ 
In  addition  to  the  coloured  body  of  the  corpuscle,  which  consists, 
as   in   mammals,    of  haemoglobin  inclosed  within  an  envelope,  there 

1  The  following  are  the  dimensions  in  parts  of  a  millimeter  of  the  coloured 
coi-puscles  of  some  oviparous  vertebrates  :  — 

Pigeon,  -         -         .         . 

Pi'og, 

Newt, 

Proteus,  ...         - 

Amphiuma,   -         -         -         - 


Long  diameter. 

Short  diatnetec 

00147 

OOO60 

0  0223 

0  0157 

0  0293 

00195 

0  0580 

0-0350 

0  0770 

0  0460 

46  THE   ESSENTIALS   OF   HISTOLOGY. 

is  a  colourless  nucleus,  also  of  an  elliptical  shape,  but  easily  becoming 
globular,  especially  if  liberated  by  any  means  from  the  corpuscle. 
The  nucleus  resembles  that  of  other  cells  in  structure,  being  bounded 
by  a  membrane  and  having  a  network  of  chromatin.     It  is  not  very 


Fig.  48. — Amphibian  erythrocytes.    (From  photographs.)    Magnified  450  diameters. 
A,  from  the  frog.  B,  from  the  toad. 

distinct  in  the  unaltered  corpuscle,  but  is  brought  clearly  into 
view  by  the  action  of  reagents,  especially  acids.  The  action  of 
reagents  upon  the  red  corpuscle  of  amphibia  is  otherwise  similar  to 
that  upon  the  mammalian  corpuscle,  water  and  acetic  acid  causing  it  to 
swell  into  a  globular  form  and  then  to  become  decolorised  ;  solution 
of  salt  causing  M^rinkling  of  the  envelope,  and  so  on.  As  a  first  effect, 
water  and  certain  other  fluids  may  cause  the  hemoglobin  to 
retire  from  the  envelope  at  the  points  where  the  fluid  is  passing 
through  the  membrane  :  a  stellate  appearance  is  thereby  often  pro- 
duced (Hiinefeldt,  Hensen).  Boric  acid  causes  the  haemoglobin  of  the 
newt's  corpuscle  to  become  partially  or  wholly  collected  around  the 
nucleus,  which  may  then  be  extruded  from  the  corpuscle  (Briicke). 

Immediately  within  the  envelope,  at  the  periphery  of  the  amphibian 
erythrocyte,  is  a  band  of  fine  fibrils  which  are  stained  by  gentian 
violet  (Meves)  and  can  also  be  seen  cut  across  in  sections  of  the 
corpuscles  (Bryce). 

The  colourless  corpuscles  of  amphibia,  although  larger,  are 
very  similar  to  those  of  mammals.  Like  them,  they  are  either 
wholly    pale    and    finely    granular    or    inclose    a    number    of    very 


ULOOD-COPvPUSCLES   OF   AMPHIBIA.  47 

distinct  grannies  of  similar  nature  to  those  met  with  in  mammals. 
These  corpuscles  vary  much  in  size  and  in  the  activity  of  their 
amoeboid  movements  :  those  which  have  a  nuiltilobular  nucleus  (fig. 
33,  b,  c)  are  usually  the  most  active.  Reagents  have  the  same  eflPect 
upon  them  as  on  those  of  mammals.  The  presence  of  glycogen  may 
be  demonstrated  in  them  by  its  reaction  with  iodine  (port-wine 
colour). 

The  blood-platelets  (thrombocytes)  in  the  frog  are  fewer  in  number 
than  in  mammals.  Many  are  of  a  spindle  shape.  They  contain 
a  nucleus-like  body  and  like  the  blood-platelets  of  mammals  they 
show  amoeboid  changes  and  tend  rapidly  to  clump  together  in 
drawn  blood. 


48 


THE  ESSENTIALS   OF  HISTOLOGY. 


LESSON    VI. 

THE  AMBCEBOID   PHENOMENA    OF  THE  COLOURLESS 
BLOOD-CORPUSCLES. 

1.  Make  a  preparation  of  blood  from  the  finger  in  the  usual  way.  Draw  a 
brush  just  moistened  with  ]3erfectly  neutral  oil  around  the  edge  of  the  cover- 
glass  to  check  evaporation.  Place  the  jjreparation  upon  a  '  warm  stage,'  and 
heat  this  to  about  the  temperature  of  the  body  (38°  C).  Bring  a  white 
corpuscle  under  observation  with  the  high  power,  and  watch  the  changes 
of  shape  which  it  undergoes.  'To  become  convinced  of  these  alterations  in 
form,  make  a  series  of  outline  sketches  of  the  same  corpuscle  at  intervals  of 
a  minute. 


Fig.  49.  — Simple  warming  app.\k.\tus,  complete,  shown  in  operation. 


The  simplest  form  of  warm  stage  is  a  copper  plate  of  about  the  size  of  an 
ordinary  slide,  perforated  in  the  centre  and  with  a  long  tongue  of  the  same 
metal  projecting  from  the  middle  of  one  edge  (fig.  49).  The  copper  plate 
rests  upon  the  stage  of  the  microscope,  with  a  piece  of  cloth  or  other  non- 
conducting material  between.  The  preparation  is  made  upon  an  ordinary 
slide  or  on  a  large  cover-glass,  which  is  placed  upon  the  warm  stage  and 


AMCEBOID  PHENOMENA  OF  COLOURLESS  CORPUSCLES.     49 

pressed  into  loiitact  witli  it  by  the  brass  clips.  Heat  is  applied  to  the  copper 
ton,i,nie  by  a  small  spirit-lamp  flame,  and  a  greater  or  less  amount  is  con- 
ducted to  the  warm  stage  and  the  superjacent  preparation  according  to  the 
point  to  which  the  flame  is  ap))lied.  To  ascertain  that  the  riglit  temperature 
is  got  and  maintained,  put  two  pieces  of  paraffin,  one  melting  at  35"  C. 
{9;")"  F.)  and  another  at  38"  C.  (100°  F.),  on  either  side  of  the  preparation. 
The  temperature  must  be  such  that  the  first  piece  is  melted  and  remains  so 
whilst  the  second  remains  unmelted.' 

2.  Mount  a  drop  of  frog's  or  newt's  blood  diluted  with  an  equal  amount  of 
salt  solution,  and  examine  it  in  the  same  manner  upon  the  copper  stage,  at 
first  cold,  afterwards  warm  ;  the  temperature  must,  however,  be  kept  l)elow 
30'  C.  Observe  the  effect  of  heat  in  acclerating  the  auKeboid  movements  of 
the  pale  corpuscles.  Sketch  one  at  intervals  of  a  minute  (a)  in  the  cold,  (b) 
whilst  warmed. 

3.  Take  some  yeast  which  has  been  mixed  with  salt  solution,  and  mix  a 
very  little  of  the  yeast  and  salt  solution  with  a  fresh  drop  of  newt's  blood, 
.slightly  oiling  the  edge  of  the  cover-glass  as  before.  Endeavour  to  observe 
the  inception  of  the  yeast-torulte  by  the  white  corpuscles.  Sketch  one  or 
two  corpuscles  containing  toruUe. 

Milk-globules  or  particles  of  carbon  or  of  vermilion  may  also  be  used  for 
this  experiment,  but  the  process  of  inception  or  'feeding'  is  most  readily 
observed  with  the  yeast  particles. 

4.  At  the  beginning  of  the  lesson  collect  a  drop  of  newt's  or  frog's  blood 
into  a  fine  capillary  tube,  seal  the  ends  of  the  tube,  and  mount  it  in  a  drop 
of  oil  of  cedar-wood  or  dammar  varnish  (or  the  clot  may  be  blown  out  into 
a  drop  of  salt  solution  on  a  slide  and  mounted  in  this  solution).  Towards  the 
end  of  the  lesson  examine  it  to  see  white  corpuscles  emigrating  from  the 
shrunken  clot  (see  fig.  50). 

5.  To  obtain  a  specimen  with  the  white  corpuscles  fixed  in  amoeboid  con- 
dition, make  a  preparation  of  newt's  blood,  mixed  with  salt  solution,  and 
set  it  aside  for  ten  minutes.  By  this  time  the  corpuscles  will  be  freely 
amoeboid,  and  will  probably  show  well-marked  pseudopodia.  To  fix  them  in 
this  condition  let  a  jet  of  steam  from  a  flask  or  kettle  play  for  two  or  three 
seconds  upon  the  covei'-glass.  The  heat  instantly  kills  the  corpuscles,  and 
they  are  fixed  in  the  form  they  presented  at  the  moment  the  steam  was 
applied.  They  may  now  be  stained  by  passing  dilute  hsemalum-  under  the 
cover-glass,  or  by  removing  the  latter  and  staining  with  eosin  and  methylene 
blue  in  the  manner  recommended  on  p.  28,  §  5.  If  hsemalum  is  used, 
the  stain  is  followed  by  dilute  glycerine,  after  which  the  cover  may  be 
cemented  and  the  preparation  kept. 


The  amoeboid  phenomena  which  are  exhibited  by  the  protoplasm 
of  the  colourless  blood-corpuscles  consist  of  spontaneous  changes  of 
form,  produced  by  the  throwing  out  of  processes  or  pseiulopodia  in 
various  directions.  When  first  thrown  out  the  pseudopodia  are  quite 
clear ;  they  appear  to  be  produced  by  a  flowing  of  the  hyaloplasm 
(see  p.  4).     If  the  corpuscle  is  stimulated,  either  mechanically,  as  by 

1  For  exact  work,  an  apparatus  somewhat  more  complex  than  the  above  is 
required.     For  description  of  such,  see  A   Course  of  Practical  Histolor/y. 

-  Delafield's  or  P]hrlich's  hematoxylin  can  he  substituted  for  htemalum  wherever 
the  latter  is  mentioned.  The  water  used  for  the  dilution  of  haematoxylin  solu- 
tions must  always  be  distilled. 

D 


50 


THE   ESSENTIALS  OF  HISTOLOGY. 


tapping  the  cover-glass,  or  electricall}',  the  pseudopodia  are  retracted, 
the  corpuscle  becoming  spherical.  A  change  of  form  caused  by  the 
protrusion  of  the  pseudopodia  maj-,  when  active,  be  followed  by 
changes  in  place  or  actual  locomotion  (migration)  of  the  corpuscle. 
When  a  pseudopodium,  or  the  external  surface  of  the  corpuscle, 
comes  in  contact  with  any  foreign  particle,  the  protoplasm  tends  to 
flow  round  and  enwrap  the  particle,  which  is  then  drawn  into  the 
corpuscle ;  particles  thus  incepted  may  be  conveyed  by  the  corpuscle 
in  its  movements  from  one  place  to  another  (fig.  51).  This  property 
plays  an  important  part  in  many  physiological  and  pathological  pro- 
cesses ;    thus    cells    in   the   spleen    resembling   large    leucocytes — the 


Fig.  .50. — White  corplscles  of  frog's  blood  iiiGRAXiNG  i-rom  shrinke.v 
CLOT  WITHIN  A  CAPILLARY  TUBE.  (Fi'om  Sanderson's  Handbook  for  the 
Ph_ysiological  Laboratorj-.) 


so-called  splenic  cells — incept  blood-corpuscles,  which  become  broken 
down  within  them  ;  and  pathogenic  bacteria  become  taken  into  the 
protoplasm  of  certain  leucocytes  (on  this  account  termed  jyhagoci/tes), 
there  to  be  destroyed  (Metchnikoff).  The  phagocytic  properties  of 
the  leucocytes  become  especially  developed  as  the  result  of  the  action 
upon  the  bacteria  of  certain  chemical  substances  which  are  present 
to  a  greater  or  less  extent  in  blood  and  which  are  termed  opsonins 
(Wright). 

It  is  probable  that  particles  of  organic  matter  which  are  taken  up 
by  the  pale  corpuscles  may  undergo  some  slow  process  of  intracellular 
digestion  within  their  protoplasm. 


AM(Ei;c>ll)  IMIENUMENA  (>F  COLUTRLESS  CORPUSCLES.     51 

The  processes  of  the  granular  corpuscles  are  quite  clear  at  first ; 
the  granules  afterwards  flow  into  them. 

The  migration  of  the  colourless  corpuscles  from  the  blood-vessels 
into  the  surrounding  tissues  (which  especially  occurs  in  inflamed 
parts),  or  from  a  blood-clot  into  the  surrounding  serum  (fig.  50),  is 
due  to  these  ama'boid  properties. 

The  conditions  which  are  favourable  to  this  amoeboid  activity  of 
the  white  corpuscles  are  (1)  the  natural  slightly  alkaline  medium, 
such  as  plasma,  serum,  or  lymph,  or  faintly  alkaline  normal  saline 
solution.  Any  increase  of  density  of  the  medium  produces  a  diminu- 
tion of  amreboid  activity,  whilst,  on  the  other  hand,  a  slight  decrease 
in  its  density  has  the  opposite  eft'ect  ;  (2)  a  certain  temperature.     In 


Fig.  51. — Changes  of  form  of  a  white  blood-corpuscle  sketched  at 
intervals  of  a  few  minutes,  showing  the  inception  of  two  small 
granules  and  the  changes  of  position  these  underwent  within 
the  corpuscle. 


warm-blooded  animals  the  phenomena  cease  below  about  10°  C.  When 
gradually  warmed  the  white  corpuscles  become  more  and  more  active 
up  to  a  certain  point,  the  maximum  being  a  few  degrees  above  the 
natural  temperature  of  the  blood.  Above  this  point  they  become 
spheroidal  and  at  a  somewhat  higher  temperature  their  protoplasm 
is  coagulated  and  killed.  Acids  at  once  kill  the  corpuscles  and  stop 
the  movements.  Xarcotic  gases  and  vapours,  such  as  carbonic  acid 
gas  or  chloroform  vapour,  also  arrest  the  movement,  but  it  recom- 
mences after  a  time  if  their  action  is  not  too  prolonged. 


52  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    VII. 
EPITHELIUM  AND  SECRETING   GLANDS. 

1.  MorxT  a  drop  of  saliva  and  examine  first  with  a  low,  afterwards  with  a 
high  power.  Observe  the  nucleated  epithelium-cells,  some  single,  and  others 
still  adhering  together  by  overlapping  edges.  Measure  three  or  four,  and 
also  their  nuclei.  Sketch  one  or  two  on  the  flat  and  one  edgeways.  Notice 
the  salivary  corpuscles,  which  are  migrated  white  blood-corpuscles,  swollen 
out  by  imbibition  of  water.  The  preparation  may  be  stained  with  diluted 
hsemalum  and  preserved  with  glycerine. 

2.  Put  a  small  shred  of  human  epidermis  into  a  drop  of  strong  caustic 
potash  solution  (35  p.c.)  for  five  minutes.  Then  break  it  up  in  water  with 
needles,  cover  and  examine.     Observe  the  now  isolated  swollen  cells. 

3.  Study  the  arrangement  of  the  cells  in  a  section  through  some  stratified 
epithelium,  such  as  that  of  the  mouth,  skin,  or  cornea.^  Notice  the  changes 
in  .shape  of  the  cells  as  they  are  ti'aced  towards  the  free  surface.  Measure 
the  thickness  of  the  epithelium.     Count  the  number  of  layers  of  cells. 

4.  Make  a  preparation  of  the  epithelium  of  the  urinary  bladder,  which 
may  be  moderately  distended  with  bichromate  of  potash  solution  (1  part  to 
800  of  salt  solution),  and  after  an  hour  or  two  cut  open  and  placed  in  moi"e 
of  the  same  solution.  Take  a  small  scraping  of  the  lining  epithelium  on  the 
point  of  a  scalpel,  and  break  it  up  by  tapping  it  in  a  drop  of  very  dilute 
hsematoxylin  on  a  slide.  Put  a  small  hair  in  the  drop  and  cover.  Add  a 
small  drop  of  glycerine  at  one  edge  :  allow  this  to  difi'use  under.  Cement 
next  day.  Observe  the  large  flat  superficial  cells,  and  the  pear-shaped  cells 
of  the  second  layer.  Sketch  one  of  each  kind.  The  cells  will  vary 
greatly  in  appearance  according  to  the  amount  of  distension  of  the  organ. 

b.  Study  the  minute  structure  of  epithelium-cells  and  their  nuclei,  both 
at  rest  and  dividing,  in  sections  of  the  skin  of  the  newt's  tail,  or  in  shreds 
of  peritoneum  or  of  epidermis  or  in  sections  of  the  salamander-tadpole.  The 
preparation  may,  for  this  purpose,  be  stained  either  with  ha?matoxylin  or 
iron-hfematoxylin,  or  with  some  aniline  dye  such  as  saff'ranin.^ 

Sketch  an  epithelium-cell  with  resting  nucleus,  and  others  with  nuclei  in 
diflPerent  phases  of  mitosis. 

The  simple  saccular  skin-glands  of  Amphibia  may  also  be  studied  in  these 
preparations. 


An  epithelium  is  a  tissue  composed  entirely  of  cells  separated  by 
a  very  small  amount  of  intercellular  substance  (cement-substance)  and 
generally  arranged  so  as  to  form  a  membrane  covering  either  an 
external  or  internal  free  surface. 

The  structure  of  epithelium-cells,  and  the  changes  which  they 
undergo  in  cell-division,  are  best  seen  in  the  epidermis  of  the  newt 

1  The  methods  of  preparing  and  staining  sections  are  given  in  the  Appendix. 


EPITHELIUM.  53 

or  of  the  salamander-tadpole  (fig.   52) ;    in  the  latter  especially,  the 
cells  and  nuclei  are  much  larger  than  in  mammals. 

Structure  of  the  cells. — Each  epithelium-cell  consists  of  protoplasm 
containing  a  nucleus.  The  protoplasm  may  either  look  granular,  or 
it  may  have  a  reticulated  appearance,  or  may  exhibit  fibrils.  The 
nucleus  is  spherical  or  ovoid.  Usually  there  is  only  one,  but  there 
may  be  two  or  more.  The  cell-substance  is  often  modified  in  its 
chemical  nature;  its  external  layer  may  become  hardened  to  form  a 


/J?  -  -  -  'H    -^ 


Fig.  52. — Epidermis  cells  of  a  lakval  salamander. 
Magnified  400  diameters.     (Wilson.) 

Thi-ee  of  the  cells  are  undergoing  division.  The  intercellular  channels  are  bridged 
across  by  fine  fibres.  At  one  place  a  branched  pigment  ceU  is  lying  between  the 
epithelium  cells. 

sort  of  membrane,  or  the  whole  cell  may  become  horny  (keratinised) ; 
or  there  may  be  a  separation  of  materials  (granules)  within  the  cell 
which  are  ultimately  used  by  the  organism,  as  in  some  secreting 
glands. 

Classification  of  epithelia. — Epithelia  are  somewhat  illogically 
classified  partly  according  to  the  shape  and  arrangement  of  the  cells, 
partly  according  to  their  function.  Thus  we  speak  of  scali/  or  pavement, 
cubical,  columnar,  glandular,  and  ciliated  epithelium.  Most  of  these 
are  simple  epithelia,  with  the  cells  only  one  layer  deep.  If  forming 
several  superposed  layers,  the  epithelium  is  said  to  be  stratified,  and 
then  the  .shape  of  the  cells  differs  in  the  different  layers.  Where 
there  are  only  three  or  four  layers  in  an  epithelium,  it  is  termed 
transitional. 


54 


THE   ESSENTIALS   OF   HISTOLOGY. 


Stratified  epithelium  covers  the  anterior  surface  of  the  cornea,  lines 
the  mouth,  pharnyx  (lower  part),  gullet,  anal  canal  and  part  of  the 
urethra,  and  forms  the  epidermis  which  covers  the  skin.  The  vocal 
cords  are  also  covered  b\'  stratified  epithelium.  In  the  female  it 
also  lines  the  vagina  and  covers  the  os  uteri.     The  cells  nearest  the 


C^ 


/ 


O 


■^^^ 


(^ 


3^ 


'%-m 


J  yj 


)  ( 


Fig.  53. — Section  of  the  stratified  epithelium  covering  the  front 
OF  the  cornea  of  the  eye  (man). 
c,  lowermost  columnar  cells ;  p,  polygonal  cells  above  these ;  fl,  flattened  cells  near  the 
surface.     Between  the  cells  are  seen  intercellular  channels  bridged  over  by  processes 
which  pass  from  coll  to  cell. 

surface  are  always  flattened  and  scale-like  (fig.  53,/;  fig.  54),  whereas 
the  deeper  cells  are  polyhedral,  and  those  of  the  deepest  layer  some- 
what columnar  in  shape  (fig.  53,  c).  Moreover,  the  deep  cells  are 
soft  and  protoplasmic,  and  are  separated  from  one  another  by  a  system 
of  intercellular  channels,  which  are  bridged  across  by  numerous  fibres 
passing   from    cell    to    cell ;    giving    the    cells,    when    separated,    the 

appearance  of  being  beset  with  short 
spines  (prickle-cells  of  Max  Schultze). 
These  '  bridging  fibres '  are  not  peculiar 
to  stratified  epithelium,  but  occur  in 
many  if  not  in  all  kinds  of  epithelia. 

The  deeper  cells  multiply  by  mitotic 
division,   the    nuclei   first  dividing  in 
Fig.  54. -Epithelium-scales  from    the    manner    already    described.     The 
™I  ?«^^^,?^  "^"^  mouth.    (Mag-    newly  formed  cells  tend  as  they  enlarge 

nified  260  diameters.)  •'  -^  ° 

to  push  those  external  to  them  nearer 
to  the  surface,  from  which  they  are  eventually  thrown  off.  As  they 
approach  the  surface  they  become  hard  and  horny,  and  in  the  case  of 
the  epidermis  entirely  lose  their  cellular  appearance,  which  can,  however, 
be  in  a  measure  restored  by  the  action  of  alkalies  (§  2).  The  cast-off 
superficial  cells  of  the  stratified  epithelium  of  the  mouth,  which  are 
seen  in  abundance  in  the  saliva  (§  1),  are  less  altered,  and  the  remains 
of  a  nucleus  is  still  visible  in  them  (fig.  54).  The  stratified  epithelium 
of  the  human  skin  (epidermis)  shows  many  peculiarities:  these  will 
be  considered  when  the  skin  itself  is  treated  of. 


TBANSITIONAL   EPITHELIUM.  55 

Transitional  epithelium  is  ;i  stratified  epithelium  consisting  of  only 
three  or  four  layers  of  cells.  It  occurs  in  the  urinary  bladder,  the 
ureter,  and  the  pelvis  of  the  kidney.  The  superficial  cells  (fig.  55,  a) 
are  large  and  flattened  ;  they  often  have  two  nuclei.  Their  free  sur- 
face is  covered  with  a  euticular  stratum  (Eggeling),  and  on  their 
under  surface  they  exhibit  depressions,  into  which  fit  the  larger 
ends  of  pyriform  cells,  which  form  the  next  layer  (fig.  55,  h). 
Between  the  tapered  ends  of  the  pyriform  cells  one  or  two  layers 
of  smaller  polyhedral  cells  are  found.  The  epithelium  seems  to  be 
renewed  by  mitotic  division  of  these  deeper  cells ;  it  is  probable  that 
the  superficial  cells  also  multiply,  but  in  this  case  by  amitosis. 


Fig.  5.5. — Epithelial  cells  from  the  bladder  of  the  rabbit.     (Klein.) 
(Magnified  500  diameters.) 

a,  large  flattened  cell  from  the  superficial  layer,  with  two  uuclei  and  with  strongly 
marked  ridges  and  intervening  depressions  on  its  under  surface ;  6,  pear-shaped  coll 
of  the  second  layer  adapted  to  a  depression  on  one  of  the  superficial  cells. 


Simple  scaly  or  pavement  epithelium  is  found  in  the  saccules  of  the 
lungs,  in  the  ducts  of  the  mammary  glands,  in  the  kidney  (in  the  tubes 
of  Henle,  lining  the  capsules  of  the  Malpighian  bodies,  and  covering 
the  glomeruli),  and  also  lining  the  cavities  of  serous  membranes 
(fig.  56),  and  the  interior  of  the  heart,  blood-vessels,  and  lymphatics. 
When  occurring  on  internal  surfaces,  such  as  those  of  the  serous 
membranes,  blood-vessels,  and  lymphatics,  it  is  often  spoken  of  as 
endothelium  or  mesothelium.  According  to  v.  Brunn  the  cells  of  a 
serous  epithelium  may  be  provided  with  a  striated  border  on  their 
free  surface,  somewhat  like  that  which  is  found  on  columnar  cells. 

Columnar  epithelium  and  ciliated  epithelium  are  for  the  most  part 
found  covering  the  inner  surface  of  mucous  membranes ;  which  are 
membranes  moistened  by  mucus  and  lining  passages  in  communication 
with  the  exterior,  such  as  the  alimentary  canal  and  the  respiratory  and 
generative  passages.     The  cells  of  a  columnar  epithelium  form  a  single 


56  THE   ESSENTIALS   OF  HISTOLOGY. 

layer,  varying  in  thickness  according  to  the  length  of  the  constituent 
cells,  and  when  the  cells  of  a  columnar  epithelium  are  short,  the 
epithelium  is  spoken  of  as  cubical,  such  as  that  which  lines  the 
vesicles  of  the  thyroid  gland. 


Fig.  56. — Pavement  epithelium  or  endothelicm  of  a  sekous  membrane. 
Nitrate  of  silver  preparation.     Carmine  staining  of  ndclei. 

Ciliated  epithelium  is  found  in  man  throughout  the  whole  extent  of 
the  air-passages  and  their  prolongations,  but  not  in  the  uppermost 
part  of  the  nostrils  which  is  supplied  by  the  olfactory  nerves, 
nor  in  the  lower  part  of  the  pharynx,  nor  in  the  terminal  bronchioles 
and  pulmonary  alveoli.  It  also  occurs  in  the  Fallopian  tubes  and 
the  greater  part  of  the  uterus ;  in  the  efferent  tubes  of  the  testicle  ; 
and  in  the  ventricles  of  the  brain,  and  the  central  canal  of  the 
spinal  cord. 

GLANDULAR  EPITHELIUM  AND  SECRETING  GLANDS. 

Glandular  epithelium  is  the  essential  tissue  of  all  the  organs  which 
are  known  as  secreting  glands.  Glands  are  of  two  chief  kinds.  Those 
which  are  best  known  and  which  are  termed  secreting  glands  proper  are 
furnished  with  a  duct  which  ramifies  in  all  parts  of  the  gland  and  by 
means  of  which  the  products  of  the  secretory  activity  of  the  gland-cells 
are  brought  to  a  free  surface.  Such  glands  have  been  developed  as 
involutions  of  the  surface  upon  which  they  open,  and  their  epithelium 
is  continuous  with  that  of  this  surface,  and  is  in  some  cases,  especially 
where  the  surface  upon  which  the  gland  opens  is  covered  with  columnar 


GLANDULAR   EPITHELIUM. 


57 


II. 


Fig.  57.— Various  kinds  of  glands. 

I.  Simple  saccular  gland  from  amphibian  skin  (Flemming).  II.  Simple  tubular  gland 
from  intestine  (Flemming).  III.  A  small  racemose  gland  with  a  single  duct  into 
which  a  number  of  irregularly  tubular  acini  open  (Flemming).  IV.  Part  of  a  tubulo- 
racemose  gland  with  the  acini  unravelled  (Flemming).  V.  Wax  model  of  a  small 
tubulo-racemose  gland  from  the  epiglottis  (Maziarski). 


58 


THE   ESSENTIALS   OF   HISTOLOGY. 


epithelium,  of  a  similar  character  to  the  epithelium  of  the  surface ;  in 
others  diiferent  in  character.  In  most  glands  the  epithelium  alters  as 
we  trace  the  duct  back  into  the  recesses  or  alveoli  of  the  gland,  and  it  is 
in  these  that  the  characteristic  glandular  cells,  which  are  generally  poly- 
hedral in  shape,  are  found.  Every  such  involution  or  ingrowth  of 
epithelium  to  form  a  gland  is,  when  first  formed,  of  a  simple  character, 


Fig.  58. — Simple  tubulak  glands  sekn  in  a  section  of  the  mucous  membrane 

OF  THE  STOJIACH  OF  THE  KANGAROO. 

t,  epithelium  of  general  surface  ;  hm,  basement  membrane  ;  n,  neck  or  duct  of  gland  ; 
6,  base  or  fundus  ;  yl,  glandular  epithelium  ;  It,  lymphoid  tissue ;  mm,  muscular 
tissue  of  the  mucous  membrane. 


shaped  like  a  test-tube  or  flask  and  filled  with  a  solid  mass  of  cells,  but 
it  presently  becomes  hollowed  out  and  the  cells  are  left  as  a  lining  to  the 
connective  tissue  membrane  which  bounds  the  involution.  The  gland 
may  remain  simple  and  unbranched  (simjyle  saccular  and  simple  tubular 
glands,  fig.  57,  I.  and  11,),  or  it  may  branch  again  and  again  until  a 
complicated  structure,  in  some  cases  small,  in  others  of  considerable  size, 
is  produced  (compound  tubular  and  compound  saccular  (or  racemose)  gla?ids 
(fig.  57,  III.,  IV.,  v.),  instances  of  which  are  furnished  by  the  kidneys 
and  salivary  glands  respectively).  The  cells  which  furnish  the  secretion 
of  the  gland  and  which  line  the  secreting  parts  of  the  tubules  of  a  tubular 


SECRETING   GLANDS.  59 

gland,  or  the  alveolar  enlai'gemonts  (acini)  at  the  ends  of  the  ducts  of  a 
racemose  gland,  are  frequently  partly  or  wholly  filled  with  graiuiles 
in  the  intervals  of  secretory  activity,  and  these  granules  become 
discharged  or  dissolved  and  pass  into  the  secretion  during  activity. 
Secreting  glands  are  always  abundantly  supplied  with  blood-vessels 
and  nerves.  The  former  are  distributed  in  the  connective  tissue  which 
holds  together  the  acini  and  groups  of  acini  (lobules)  of  the  gland ; 
the  latter  are  supplied  partly  to  the  blood-vessels  and  partly  ramify 
amongst  the  secretory  epithelium  cells. 

The  liver  differs  from  all  other  secreting  glands  in  being  composed  of 
solid  masses  of  cells  (hepatic  lobules)  instead  of  tubular  acini  lined  by 
epithelium.  It  exhibits  also  other  important  differences  in  the  nature 
of  its  blood-supply  and  the  relation  between  the  blood  and  the  liver- 
cells. 

The  other  kind  of  secreting  glands,  known  as  the  internally  secreting 
glands,  are  not  furnished  with  ducts  and  are  usually  described  (along 
with  the  spleen  and  the  lymphoid  structures)  as  ductless  glands.  The 
internally  secreting  glands  are,  like  the  externally  secreting  organs, 
composed  of  epithelial  cells,  sometimes  grouped  in  solid  masses  {e.g. 
suprarenal  gland),  in  other  cases  disposed  around  hollow  vesicles  (e.g. 
thyroid)  which  become  filled  with  the  material  of  the  secretion.  But 
as  in  these  glands  there  is  no  duct  the  secretion  is  carried  into  the 
blood  either  directly  by  the  blood-vessels  of  the  gland  or  indirectly 
through  the  lymphatics. 

The  detailed  study  of  the  glands  and  of  other  epithelial  structures 
may  be  reserved  until  the  organs  in  which  they  occur  are  described, 
but  columnar  and  ciliated  epithelia  will  be  dealt  with  in  the  next 
Lesson. 

The  hairs  and  nails  and  the  enamel  of  the  teeth  are  modified 
epithelial  tissues.  They  will  be  described  along  with  the  skin  and 
structures  connected  with  the  mouth  respectively. 


60  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON   VIII. 

COLUMXAR  ASD   CILIATED  EPITHELIUM:   ACTION   OF  CILIA. 

1.  Break  up  in  dilute  glycerine  a  shred  of  epithelium  from  a  minute  piece 
of  the  mucous  membrane  of  intestine  (frog)  that  has  been  treated  with  1  per 
cent,  osmic  acid  for  some  hours,  and  has  subsequently  macerated  in  water 
for  a  few  days.  The  cells  easily  separate  on  tapping  the  cover-glass. 
Measure  and  sketch  one  or  two  cells. 

The  cover-glass  may  be  at  once  fixed  by  gold  size. 

2  Prepare  ciliated  epithelium  from  a  trachea  that  has  been  in  chromic 
acid  solution  (1  to  2000  normal  saline)  for  a  few  days,  in  the  same  way  as 
with  transitional  epithelium  (.^  4,  p.  52).  Measure  in  one  or  two  of  the 
cells  (a)  the  length  of  the  cells,  (h)  the  length  of  the  cilia,  (c)  the  size  of  the 
nucleus.     Sketch  two  or  three  cells. 

3.  Mount  in  sea-water  one  or  two  bars  of  the  gill  of  the  marine  mussel 
(fig.  59).  Study  the  action  of  the  large  cilia.  Now  place  the  preparation 
upon  the  copper  warm  stage  (see  Lesson  VI.)  and  observe  the  effect  of  raising 
the  tempei-ature. 


Fig.  59. — Valve  of  mussel  (mttilus  edclis)  showing  Ir,  Ir,  the  expanded 

GILLS  OB   BKAXCHI.E,  WHICH,    OWING    TO   THE   LITTLE   BARS   OF  WHICH    THEY 
ARE  COMPOSED,  PRESENT  A  STRIATED  ASPECT. 

ml,  mantle ;  m,  cut  adductor  muscle  ;  !,  mass  of  viscera ;  the  dark  projection  just  above 

is  the  foot. 

Keep  this  preparation  until  the  end  of  the  lesson,  by  which  time  many  of 
the  cilia  will  have  become  languid.  "When  this  is  the  case  pass  a  drop  of 
dilute  potash  solution  (1  part  KHO  to  lO'X)  of  sea-water)  under  the  cover- 
glass  and  observe  the  effect. 

4.  Cement  with  sealing-wax  a  piece  of  small  glass  tubing  to  a  slide  so  that 
one  end  of  the  tube  comes  nearly  to  the  centre  of  the  slide.  To  do  this 
effectually  the  slide  must  be  heated  and  some  sealing-wax  melted  on  to  it 
and  allowed  to  cool.  The  glass  tube  is  then  made  hot  and  applied  to  the 
slide,  embedding  itself   as  it   does  so   in   the  sealing-wax.     Apply  a  ring 


COLUMNAR  AND  CILIATED   EPITHELIUM. 


61 


of  putty  or  modelling  wax  (half  an  inch  in  diameter  and  rising  above  the 
glass  tube)  so  as  to  include  the  end  of  the  tube.  Make  a  deep  notch  in  the 
ring  opposite  the  tube  for  the  exit  of  the  gas.  Place  a  drop  of  water 
within  the  ring  (fig.  60). 


Fig.  60.— Moist  chamber  adapted  for  passing  a  gas  or  vapour  to  a 
preparation  under  the  microscope. 

Put  a  bar  from  the  gill  upon  a  cover-glass  in  the  least  possible  quantity  of 
sea-water  ;  invert  the  cover-glass  over  the  putty  ring,  and  press  it  gently 
and  evenly  down.  The  preparation  hangs  in  a  -moist  chamber  within  which 
it  can  be  studied  through  the  cover-glass,  and  into  which  gases  or  vapours 
can  be  passed  and  their  effects  observed. 


Fig.  61. — Method  of  subjecting  a  preparation  to  a  .stream  of  carbon 

DIOXIDE. 
6,  bottle  containing  marble  and  hydrochloric  acid  ;  h',  wash-bottle,  connected  by  india- 
rubber  tube,  t,  with  the  moist  chamber,  a. 

Pass  C0.2  through  the  chamber,  and  after  observing  the  eflfect  replace  it  by 
air  (see  fig.  61).     Eepeat  with  ether  and  with  chloroform  vapour. 


Columnar  epithelium. — The  cells  of  a  columnar  epithelium  (fig.  62) 
are  prismatic  columns,  which  are  set  closely  side  by  side,  so  that  when 
seen  from  the  surface  a  mosaic  appearance  is  produced.     They  often 


62 


THE   ESSENTIALS  OF   HISTOLOGY. 


taper    somewhat    towards    their    attached    end,    which    is    generally 
truncated,  and  set  upon  a  basement  membrane.     Their  free  surface  is 


Fig.  62. 


Fig.  63. 


Fig.  62.— a  row  of  columnar  cells  from  the  intestine  of  the  rabbit. 

Smaller  cells  are  seen  between  the  epithelium-cells  ;  these  are  leucocytes. 

Fig.  63.— Columnar  epithelium-cells  of  the  rabbit's  intestine. 
The  cells  have  been  isolated  after  maceration  in  very  weak  chromic  acid.  The  cells  are 
much  vacuolated,  and  one  of  them  has  a  fat-globule  adhering  to  it  near  its  attached 
end  ;  the  striated  border  (.sf;)  is  well  seen,  and  the  bright  disk  separating  it  from 
the  cell-protoplasm  ;  n,  nucleus,  with  intranuclear  network  ;  a,  a  thinned-out  wing- 
like projection  of  the  cell  which  probably  fitted  between  two  adjacent  cells. 


•■.'t© 


&■ 


Fig.  6o. 


Fig.  64. 


Fig.  66. 


Fig.  64. — A  columnar  epithelium-cell,  showing  mass  of  fibrils  (cytomitome)' 
within  the  cytoplasm.     (M.  Heidenbain.) 

Fig.  65. — A  goblet  or  mucus-secreting  cell  in  columnar 

epithelium.     (M.  Heidenbain.) 

The  centrosome  is  in  the  mucigen-mass.     An  ordinary  columnar  cell  is  also  shown. 

Fig.  66. — Ciliated  columnar  epithelium,  from  the  trachea  of  a  babbit. 

9)ii,  m-,  m^,  mucus-secreting  cells  in  various  stages  of  mucigon  formation.     The  prepara- 
tion was  treated  with  dilute  chromic  acid. 

covered  by  a  thick  striated  border  (fig.  63,  str.)  which  may  sometimes 
become  detached  in  teased  preparations.  The  protoplasm  of  the  cell 
is  highly  vacuolated  and  reticular,  and  fine  longitudinal  stride  may  be 


COLUMNAR  EPITHELIUM. 


63 


seen  in  it,  M'hich  appear  continuous  with  the  striae  of  the  free  bordei'. 
Between  the  striated  border  and  the  protoplasm  of  the  cell  is  a  highly 
refracting  disk  which  contains  fine  dumb-bell  shaped  particles  set 
vertically,  connected  below  with  the  fibrils  or  striie  which  run  through 
the  cell  protoplasm  (fig.  64,  65).  It  has  been  suggested  that  these 
particles  are  formed  by  multiplication  of  the  centrosome,  but  the 
fact  cannot  be  regarded  as  established.  The  nucleus  is  ovoid  and 
reticular.  The  lateral  borders  of  the  cells 
are  often  somewhat  irregular  or  jagged, 
the  result  of  the  presence  of  amosboid 
cells,  which  are  generally  found  between 
the  columnar  cells,  at  least  in  the  intes- 
tine. After  a  meal  containing  fat  the 
epithelium-cells  of  the  small  intestine  con- 
tain fat  globules,  which  become  stained 
black  in  osmic  preparations. 

Columnar  epithelium-cells  are  found 
lining  the  whole  of  the  interior  of  the 
stomach  and  intestines :  they  are  also 
present  in  the  ducts  of  most  glands,  and 
sometiriies  also  in  their  secreting  tubes 
and  saccules.  The  epithelium  which 
covers  the  ovary  is  also  of  a  modified 
columnar  shape,  but  cells  having  all  the 
structural  peculiarities  indicated  above 
are  found  only  in  the  alimentary  canal 
and  in  its  diverticula. 

Goblet-cells.  —  Some  of  the  cells  of  a 
columnar  epithelium,  and  also  cells  of 
glandular,  ciliated,  and  transitional  epi- 
thelia,  contain  mucigen,  which  is  laid 
down  within  the  cell  in  the  form  of 
granules  (fig.  65,  fig.  66,  w\  «?- ;  fig.  67). 
swell  up  to  form  globular  masses  which  may  run  together  and  greatly 
distend  the  part  of  the  cell  nearest  the  free  border.  When  the 
mucigen  is  extruded  as  mucus  the  cell  takes  the  form  of  an  open 
cup  or  chalice  (fig.  66,  m^),  hence  the  name. 

These  goblet-cells,  or,  as  they  are  more  appropriately  termed,  mums- 
secreting  cells,  are  probably  not  mere  temporary  modifications  of  the 
ordinary  columnar  and  ciliated  cells  amongst  which  they  are  found,  but 
permanently  differentiated  cells,  which,  after  having  got  rid  of  their 
mucus  by  extrusion,  again  form  a  fresh  supply  in  the  same  way  as 


Fig.  67.— Three  mucus-secret- 
ing CELLS  FROM  THE  STOMACH, 
FILLED  WITH  MUCIGEN  GRAN- 
ULES, SOME  OF  WHICH  ARE  IN 
PROCESS     OF     EXTRUSION.        (M. 

Heidenliain.) 

These  granules  eventually 


64 


THE   ESSENTIALS   OF   HISTOLOGY. 


before.  In  the  gastric  mucous  membrane  all  the  surface  epithelium  is 
composed  of  mucus-secreting  cells,  and  they  extend  also  into  the  mouths 
of  the  glands.  In  the  large  intestine  also  most  of  the  cells  both  of  the 
surface  and  in  the  glands  are  goblet-cells.  According  to  the  observations 
of  Carlier  those  of  the  gastric  mucous  membrane  are  connected  together 
laterally  by  protoplasmic  fibres. 

Ciliated     epithelium.  —  The 
y>\-  ^    cells  of  a  ciliated  epithelium  are 

usually  columnar  in  shape  (figs. 
66,  68),  but  in  place  of  the 
striated  border  of  the  ordinary 
columnar  cell  the  free  surface  is 
surmounted  by  a  bunch  of  fine 
tapering  filaments  {vibratile  cilia), 
which,  during  life,  move  spon- 
taneously to  and  fro,  and  serve 
to  produce  a  current  in  the  fluid 
which  covers  them.  The  border 
upon  which  the  cilia  are  set  is 
bright  in  the  living  condition : 
after  fixation  it  appears  formed 
of  little  juxtaposed  knobs  or  basal 
particles,  to  each  of  which  a 
cilium  is  attached. 

In  the  large  ciliated  cells  which 
line  the  alimentary  canal  of  .some 
molluscs  (fig.s.  68,  70),  and  with  less 
distinctness  in  the  ciliated  cells  of 
vertebrates,  the  knob  may  be  ob- 
served to  be  prolonged  into  the 
protoplasm  of  the  cell  as  a  fine 
varicose  filament,  termed  the  rootlet 
of  the  cilium.  .Since  the  axial  fibril 
in  the  tail  of  the  spermatozoon  (which  is  commonly  regarded  as  a  cilium) 
is  developed  in  connection  with  the  centrosome,  it  has  been  supposed 
that  the  cilia  of  an  ordinary  ciliated  cell  may  also  be  outgrowths  from 
the  (multiplied)  centrosome.  But  although  it  may  be  the  case  that  the 
basal  i^articles  are  formed  by  the  division  of  the  centrosome  of  the  cell,  in 
which  case  the  rootlets  may  represent  the  fibrils  of  archoplasm  which 
radiate  from  the  centrosome  of  such  a  cell  as  the  white  corpuscle  (fig.  9),  it 
appears  not  to  be  true  that  the  cilia  are  developed  from  these  basal  par- 
ticles, for  the  cilia  sometimes  appear  before  the  basal  particles.  In  plant 
spores,  which  have  no  centrosomes,  the  cilia  are  developed  from  amoeboid 
processes  of  the  ectoplasm  of  the  cell  (Strassburger).  Similar  basal  particles 
and  longitudinal  fibrils  are  found  in  columnar  cells  (pp.  62,  63),  and  these 
are  probably  homologous  with  the  knobs  and  rootlets  of  the  ciliated  cell, 
while  the  bunch  of  cilia  of  the  latter  is  represented  by  the  striated  border 
of  the  columnar  cell. 


Fig.  68. 


-Four  cili.\ted  cells. 
(Lenhossek. ) 


CILIATED   EPITHELIUM. 


65 


Schuberg  has  described  in  the  cilia  of  certain  infusoria  an  end-piece  whicli 
stains  ditt'erently  from  tlie  rest  of  the  ciliuni  (tig  71). 

The  action  of  cilia.— When  in  motion  a  cilium  is  bent  quickly  over 
in  one  direction  with  a  lashing  whip-like  movement,  immediately 
recovering  itself.  When  vigorous  the  action  is  so  rapid,  and  the 
rhythm  so  frequent  (ten  or  more  times  in  a  second),  that  it  is  im- 


FiG.  69.— Columnar  ciliated 

EPITHELIUM-CELLS  FROM  THE 
LOWER  PART  OF  THE  HUJIAN 
NASAL  PASSAGES.       EXAMINED 

FRESH  IN  SERUM.     (Sharpey.) 


s  %& 


Fig.  71- — Cilia  of  frontonia  leucas. 

(A.  Schuberg.) 

Loffler's  flagellum  stain,      x  22.50. 


Fig.  70.— Ciliated  cell,  from 

THE  intestine  OF  A  MOLLUSC. 
(Engelmann.) 


possible  to  follow  the  motion  with  the  eye.  All  the  cilia  upon  a 
ciliated  surface  are  not  in  action  at  the  same  instant,  but  the  move- 
ment travels  in  weaves  over  the  surface.  If  a  cell  is  detached  from 
the  general  surface,  its  cilia  continue  to  act  for  a  while,  but  their 
movement  at  once  ceases  if  they  are  detached  from  the  cell.  If, 
however,  a  portion  of  the  cell  protoplasm  is  detached  with  them, 
they  will  continue  to  move  for  a  time. 

The  rhythm  is  slowed  by  cold,   quickened  by   warmth ;  but  heat 

E 


66  THE   ESSENTIALS  OF  HISTOLOGY. 

beyond  a  certain  point  kills  the  cells.  The  movement  will  continue 
for  some  time  in  water  deprived  of  oxygen.  Both  CO.,  gas  and 
ether  and  chloroform  vapour  arrest  the  action,  but  it  recommences 
on  restoring  air,  if  their  action  is  not  too  prolonged.  Dilute  alkaline 
solutions  quicken  the  activity  of  cilia,  or  may  even  restore  it  shortly 
after  it  has  ceased. 

Theories  of  ciliary  action. — Various  attempts  have  been  made  to  explain 
the  manner  in  which  cilia  act.  One  hypothesis  supposes  that  one  side  only 
of  eacli  ciliura  is  contractile,  the  other  side  being  elastic,  or  that  there  is  a 
more  rigid  but  elastic  axis  and  a  contractile  covering.  This  supposition  is 
negatived  by  the  fact  that  in  heat  rigor  the  cilia  are  not  bent  over  as  they 
would  be  by  the  contraction  whicli  always  accomjjanies  rigor,  but  stand  up 
straight.  It  is  moreover  impossible  to  suppose  that  a  soft  structure  like  a 
ciliiim  could  be  bent  over  in  a  uniform  gentle  curve  by  contraction  along  one 
side  ;  such  contraction  could  only  produce  shortening  and  wrinkling  of  the 
cilium,  effects  which  are  never  observed.  Another  hypothesis  assumes  that 
the  projecting  cilia  are  set  in  action  by  rhythmic  lateral  contractions  in  the 
protoplasm  ;  which,  by  moving  the  rootlets,  cause  the  cilia  to  bend  over  as  a 
whip  is  bent  by  movements  of  the  wrist  applied  to  its  handle.  But  this 
again  implies  an  amount  of  rigidity  wh'ch  cilia  do  not  possess,  for  it  must 
be  borne  in  mind  that  they  have  to  overcome  the  resistance  of  fluid,  and  of 
fluid  which  is  in  many  cases  highly  viscous. 

If  in  our  ignorance  of  the  structure  of  the  individual  cilia  we  are  to  form 
an  idea  as  to  the  cause  of  the  rhythmical  bending  over  of  these  minute  cell 
processes,  the  simplest  hypothesis  appears  to  be  to  assume  that  they  are 
curved  flattened  hollow  filaments,  the  interior  communicating  with  the  cell- 
protoplasm.^  If  this  is  the  case,  then  rhythmical  variations  of  pressure 
within  the  cell-protoplasm,  which  might,  as  in  the  case  of  amoeboid  move- 
ments, be  caused  by  alterations  in  surface  tension,  would  be  transmitted  to 
the  cilia  and  wouM  cause  the  curve  to  open  out,  and  again  to  assert  itself, 
according  to  the  degree  of  tension  within  the  tubular  filament.  Such  action 
can  be  imitated  with  a  fine  curved  and  flattened  indiarubber  tube  attached 
to  a  pressure  bag.  Any  increase  of  pressure  within  the  tuV>e  causes  it  to 
straighten  out ;  on  again  decreasing  the  pressure  the  tube  bends  over 
exactly  in  the  manner  of  a  cilium.  This  hypothesis  has  the  advantage  over 
the  others  which  have  been  oflered  that  it  explains  the  movements  of  cilia 
on  a  theory  which  is  precisely  similar  to  that  which  gives  the  most  probable 
explanation  of  amieboid  movements  of  protoplasm,  viz.,  that  they  are  due 
to  variations  in  surface  tension,  and  it  thus  brings  these  two  forms 
of  protoplasmic  activity  into  line  with  one  another.  It  will  presently  be 
shown  that  the  changes  which  occur  in  muscle  in  contraction  are  suscep- 
tible of  a  similar  explanation. 

^All  cilia  and  cilium-like  structures  (flagella)  which  are  sufficiently  large  to 
show  any  structural  differentiation,  exhibit  au  external  membranous  covering 
and  a  clear  and  usually  structureless  contents,  but  the  minute  size  of  ordinary 
cilia   prevents  one  from  determining  whether  this  is  also  the  case  with  them. 


THE  CONNECTIVE   TISSUES.  67 


LESSON    IX. 

THE  CONNECTIVE  TISSUES. 
AREOLAR  AND  ADIPOSE  TISSUE.     RETIFORM  TISSUE. 

1.  Take  a  little  of  the  subcutaneous  tissue  or  of  the  intermuscular  connective 
tissue  of  a  rabbit  or  guinea-pig  and  spread  it  out  with  needles  on  a  dry  slide 
into  a  large  thin  film.  Keep  the  centre  moist  by  occasionally  breathing  on 
it,  but  allow  the  edges  to  dry  to  the  slide.  Before  commencing  put  a  drop 
of  salt  solution  on  a  cover-glass,  and  now  invert  this  over  the  film.  Examine 
with  a  high  power.  Sketch  one  or  two  bundles  of  white  fibres  and  also  one 
or  two  elastic  fibres,  distinguishable  from  the  former  by  their  sharp  outline, 
isolated  course,  and  by  their  branching.  Sketch  also  one  or  more  connective- 
tissue  corpuscles,  if  any  such  are  visible  in  the  clear  interspaces.  Look  also 
for  migratory  cells  (leucocytes).  Ne.Kt  carefully  remove  the  cover-glass  and 
replace  the  salt  solution  by  dilute  acetic  acid  (1  per  cent.).  Watch  its  effect 
in  swelling  the  white  fibres  and  bringing  more  clearly  into  view  the  elastic 
fibres  and  corpuscles.     Look  for  constricted  bundles  of  white  fibres. 

2.  Make  another  very  thin  film  in  the  same  way,  but  allow  to  dry  com- 
pletely. Pour  over  the  film  a  1  per  cent,  solution  of  magenta  in  50  per  cent, 
alcohol,  to  which  1  drop  per  cubic  centimeter  of  a  1  per  cent,  .solution  of 
gentian  violet  in  alcohol  has  just  been  added.  After  one  minute  drain  this 
otf,  wipe  round  the  specimen  and  allow  the  remainder  of  the  staining  solution 
to  dry  on  the  film.  When  completely  dry  mount  in  dammar.  The  elastic 
fibres  are  deeply  stained  ;  the  cells  are  also  well  shown. 

3.  Prepare  another  film  of  the  subcutaneous  tissue,  including  a  little 
adipose  tissue.  Fix  by  pouring  over  it  formol  (10  p.c.)  and  leave  this  in 
contact  with  the  film  for  20  minutes.  Wash  with  water  and  stain  with 
saturated  solution  of  Sudan  III.  or  Scharlach  R.  in  75  p.c.  alcohol  ;  wash 
with  75  p.c.  alcohol  to  remove  stain  from  everything  except  fat,  then  wash 
with  water  and  stain  with  dilute  hsematoxylin.  Mount  in  glycerine  and 
water.  Examine  first  with  a  low  and  afterwards  with  a  high  power.  The 
fat  is  well  brought  out  by  the  Sudan  III.  or  Scharlach  R.  stain  ;  if  the 
preparation  is  from  a  young  animal,  fat-cells  will  be  found  in  process  of 
formation.     Measure  and  sketch  two  or  three  of  the  cells. 

The  fat  may  also  be  stained,  without  prior  fixation,  by  treatment  with 
1  p.c.  osmic  acid  solution. 

4.  Spread  out  another  large  film  of  connective  tissue,  letting  its  edges  dry 
to  the  slide,  but  keeping  the  centre  moist  by  the  breath.  Place  on  its  centre 
a  large  drop  of  nitrate  of  silver  solution  (1  per  cent.).  After  five  minutes 
wash  this  away  with  distilled  water,  and  expose  to  direct  sunlight  until 
stained  brown.  Now  allow  the  film  to  dry  completely,  and  cover  it  in 
dammar  varnish  or  Canada  balsam  dissolved  in  xylol.  Sketch  the  outlines 
of  two  or  three  of  the  cell-spaces. 

5.  To  display  retiform  tissue  the  following  method  is  recommended 
(Spalteholz).     Place  a  piece  of  the  organ  {e.g.  lymphatic  gland)  for  twenty- 


68  THE   ESSENTIALS  OF   HISTOLOGY. 

four  hours  or  more  in  alcohol,  then  overnight  at  38°  C.  in  a  1  per  cent, 
solution  of  carbonate  of  soda  to  which  a  few  drops  of  a  solution  containing 
trypsin  have  been  added.  Cautiously  transfer  the  semi-digested  structure 
to  alcohol  again,  and  leave  it  for  a  few  hours.  Embed  in  paraffin  in  the 
usual  way  and  stain  the  sections  with  iron  lipematoxylin.  The  fibrils  of 
connective  and  retiform  tissue  are  the  only  structures  which  have  remained 
undigested  and  they  are  deeply  coloured  by  the  hasmatoxylin. 

The  connective  tissues  include  areolar  tissue,  adipose  tissue,  elastic 
tissue,  fibrous  tissue,  reticular  and  lymphoid  tissue,  cartilage  and  bone. 
All  these  tissues  agree  in  certain  microscopical  and  chemical  characters. 
They,  for  the  most  part,  have  a  large  amount  of  intercellular  substance 
in  which  fibres  are  developed,  and  these  fibres  are  of  two  kinds — white 
and  yellow  or  elastic.  Moreover,  there  are  many  points  of  similarity 
between  the  cells  which  occur  in  these  tissues ;  they  are  all  developed 
from  the  same  embryonic  formation,  and  they  tend  to  pass  imper- 
ceptibly the  one  into  the  other.  Besides  this,  the  use  of  these  several 
tissues  is  similar;  they  mostlj^  serve  to  connect  and  support  the 
other  tissues,  performing  thus  a  passive  mechanical  function.  They 
may  therefore  be  grouped  together,  although  differing  considerably 
in  external  and  even  in  microscopic  characters.  Of  the  connective 
tissues,  however,  there  are  three  which  are  so  intimately  allied  as 
to  be  naturally  considered  together,  being  composed  of  exactlj^  the 
same  elements,  although  differing  in  the  relative  development  of  those 
elements  :  these  are  the  areolar,  elastic,  and  fibrous  tissues.  Adipose 
tissue  and  reticular  tissue  may  both  be  looked  upon  as  special  modi- 
fications of  areolar  tissue.  Areolar  tissue  being  the  commonest  and, 
in  a  sense,  the  most  typical,  its  structure  may  be  considered  first. 

Areolar  tissue. — The  areolar  tissue  presents  to  the  naked  eye  an 
appearance  of  fine  transparent  threads  and  laminae  which  intercross  in 
every  direction  with  one  another,  leaving  intercommunicating  meshes, 
or  areolae,  between  them.  When  examined  with  the  microscope,  these 
threads  and  fibres  are  seen  to  be  principally  made  up  of  wavy  bundles  of 
exquisitely  fine  transparent  fibres  {tchite  fibres,  fig.  73,  A).  The  bundles 
run  in  different  directions,  and  may  branch  and  intercommunicate  with 
one  another  (fig.  75);  but  the  individual  fibres,  although  they  pass  from 
one  bundle  to  another,  never  branch  or  join  other  fibres.  The  fibres 
are  cemented  together  into  the  bundles  by  a  clear  substance  containing 
mucin,  and  the  same  clear  material  forms  also  the  basis  or  ground- 
substance  of  the  tissue,  in  which  the  bundles  themselves  course,  and  in 
which  also  the  corpuscles  of  the  tissue  lie  embedded.  This  ground- 
substance  between  the  bundles  can  with  difficulty  be  seen  in  the  fresh 
tissue  on  account  of  its  extreme  transparency  ;  but  it  can  be  biought  to 
view  by  staining  with  nitrate  of  silver,  as  in  §  4.     The  whole  of  the 


AREOLAR  TISSUE. 


69 


tissue  is  thereby  stained  of  a  yellowish  brown  colour,  with  the  excep- 
tion of  the  spaces  which  are  occupied  by  the  corpuscles  (cell-spaces). 


Fig.  72.    Ground  substance  of  connective  tissue  stained  by  silver. 
The  cell-spaces  are  unstained.     From  a  photograph.    Magnified  250  diameters. 


Fig.  73.— White  and  elastic  fibres  of  areolar  tissue. 
A,  bundles  of  white  fibres  partly  unravelled.     B,  elastic  fibres. 

As  Macallum  has  shown,  this  reaction  is  due  to  the  presence  of  chlorides 
in  the  intercellular  substance,  whereas  the  cell-protoplasm  contains 
none. 

Besides  the  white  fibres  of  connective  tissue  here  described,  fibres 
of  a  different  kind  (fig.  73,  B)  may  be  made  out  in  the  preparations; 
these  are  the  elastic  fibres.    They  are  especially  well  seen  after  treatment 


70  THE   ESSENTIALS   OF   HISTOLOGY. 

with  acetic  acid,  and  after  staining  with  magenta,  or,  in  sections, 
with  orcein ;  but  thej'  can  be  detected  also  in  the  fresh  preparation. 
They  are  characterised  by  their  distinct  outline,  their  straight  course, 
the  fact  that  they  never  run  in  bundles,  but  singly,  and  that  they 
branch  or  join  neighbouring  fibres.  If  V^roken  by  the  needles  in 
making  the  preparation,  the  elastic  recoil  causes  them  to  curl  up, 
especially  near  the  broken  ends.  Besides  these  histological  differ 
ences,  the  two  kinds  of  fibres  differ  also  in  their  chemical  characters. 
Thus  the  white  fibres  are  formed  of  a  material  {collagen)  which  is  dis- 
solved by  boiling  in  water  yielding  gelatin,  and  by  peptic  digestion, 
but  is  not  dissolved  by  tryptic  digestion  ;  whereas  the  substance  of 
which  the  elastic  fibres  are  composed  (elastin)  resists  for  a  long  time 
the  action  of  boiling  water  and  peptic  digestion,  although  it  is  dis- 
solved   by  tryptic  digestion.     Moreover,   the  white   fibres  swell  and 


Fig.  74. — A  white  bundle  swollen  by  acetic  acid.    From  the  scbakachnoid 

TI.SSUE  AT  the  BASE  OK  THE  BRAIN.      (Toldt. ) 

become  indistinct  under  the  action  of  acetic  acid  ;  the  elastic  fibres 
are  unaltered  by  this  reagent.  Elastic  fibres  appear  to  have  a  sheath 
which  is  more  resistant  to  reagents  than  the  rest  of  the  fibre. 

The  bundles  of  white  fibres  which  have  been  swollen  out  by  acid 
sometimes  exhibit  constrictions  at  irregular  intervals  (fig.  74).  These 
are  in  many  instances  due  to  elastic  fibres  coiling  round  the  white 
bundles. 

The  cells  of  areolar  tissue. — Several  varieties  of  connective  tissue 
cells  are  distinguished,  viz.  :  (I)  Lamellar  cells,  which  are  flattened 
and  often  branched  (fig.  75,  c,  c')  and  may  be  united  one  to  the 
other  by  their  branches,  as  in  the  cornea.  Sometimes  they  are 
unbranched  and  may  lie  along  the  fibril-bundles  and  even  themselves 
show  a  fibrillar  appearance.  Some  authors  have  inferred  from  this 
that  these  cells  are  transformed  into  white  fibril-bundles  and  have 
termed  them  "  fibroplasts  "  ;  but  the  fibrillation  which  tbey  exhibit  is 
not  of  the  same  character  as  that  of  the  white  fibres,  and  is  pro- 
bably a  form  of  cytomitome,  such  as  is  seen  in  many  protoplasmic 
cells.      In     certain     situations    the    lamellar    connective-tissue    cells 


THE   CELLS   OF   ARKOLAR  TISSUE. 


71 


Fig.  75.— Subcutaneous  tissue  from  a  young  rabbit,  PREPAREn  as  directed 

IN  §  1.     Highly  magnified. 

The  white  fibres  are  in  wavy  bundles ;  the  elastic  fibres  form  an  open  network,     p,  p, 
plasma-cells  ;  g,  granule-cell ;  c,  c',  lamellar-cells  ;  /,  fibrillated-cell. 


Fig.  76. — Epithelioid  cells  of  connective  tissue  from  the  surface  of 
AN  aponeurosis.     (Nitrate  of  silver  preparation.) 


72 


THE   ESSENTIALS   OF  HISTOLOGY 


are  greatly  flattened  out,  especially  when  they  lie  upon  the  surface  of 
aponeuroses  and  they  are  there  joined  edge  to  edge  like  the  cells  of  an 
endothelium  (fig.  76.  The  apparent  cell-spaces  in  silver  preparations 
have  of  course  in  all  cases  a  similar  arrangement  to  that  of  the  cells). 
(2)  Plasma  cells  (fig.  75,  p),  which  are  composed  of  a  soft  much- 
vacuolated  protoplasm,  rarely  flattened,  but  otherwise  varying 
greatly  in  shape  and  size.  (3)  Granular  cells  (g)  {Mast-zellen  of  Ehrlich, 
clasmatocj/tes  of  Ranvier),  usually  spheroidal  or  ovoidal  in  shape,  and 
formed,  like  the  plasma-cells,  of  soft  protoplasm,  but  thickly  occupied 
with  albuminous  granules,  which  are  deeply  stained  by  gentian  violet 


Fig.  77.- -A  pew  cells  from  the  margin  of  a  fat  lobule.     Highly  magnified. 
From  a  photograph. 
f.g.  fat-globule  distending  a  fat-cell ;  u,  nucleus  ;  m,  membranous  envelope  of  the  fat- 
cell  ;  c.  r.  bunch  of  crystals  within  a  fat-cell ;  c,  capillary  vessel ;  )',  venule  ;  c.t.  con- 
nective-tissue cell ;  (I,  granular  cell ;  the  connective-tissue  fibres  are  not  represented. 

and  by  other  basic  aniline  dyes.  (4)  Migratory  leucocytes  may  also  be 
seen  here  and  there  in  the  areolar  tissue  {wander-cells).  (5)  In  the  middle 
coat  of  the  eye  in  mammals,  and  in  some  parts  of  the  skin,  some  of  the 
connective-tissue  cells  are  filled  with  granules  of  pigment  (pigment-cells). 

These  are  much  more  extensively  present  in  lower  vertebrates,  especially 
in  amphibia  and  fishes,  where  they  exhibit  amoeboid  changes  which  result  in 
the  pigment  being  at  one  time  diffused  over  a  considerable  area  and  at 
another  time  restricted  to  the  immediate  neighbourhood  of  the  nucleus. 
The  changes  thus  produced  cause  alteration  in  the  general  colour  and  shade 
of  the  integument,  where  such  pigment  cells  are  very  numerous,  and  serve 
the  purpose  of  protective  adaptation  of  the  animals  to  their  environment. 

The  cells  lie  in  spaces  in  the  ground-substance,  between  the  bundles 
of  white  fibres.      In   some  parts  of  the  connective  tissue  the  white 


THE   CELLS   OF   AREOLAR  TISSUE. 


bundles  are  developed  to  such  an  extent  as  to  pervade  almost  the 
whole  of  the  ground-substance,  and  then  the  connective-tissue  corpuscles 
become  squeezed  into  the  interstices,  flattened  lamellar  expansions  of 
the  cells  extending  between  the  bundles,  as  in  tendon  (see  next  Lesson). 

A" 


nr 


Fig.  78. — Deposition  of  f.\t  in  connective-tissue  cells. 

/,  a  cell  with  a  few  isolated  fat-droplets  in  its  protoplasm  ;  f,  a  cell  with  a  single  large 
and  several  minute  drops ;  /",  fusion  of  two  large  drops  ;  g,  granular  cell,  not  yet 
exhibiting  any  fat-deposition  ;  c.t.,  flat  connective-tissue  corpuscle  ;  c,  c,  network  of 
capillaries. 

The  cells  and  cell-spaces  of  areolar  tissue  come  into  intimate  relation 
Avith  the  cells  lining  the  lymphatic  vessels  and  small  blood-vessels. 
This  connection  can  best  be  seen  in 
silvered  preparations  ;  it  will  be 
again  referred  to  in  speaking  of  the 
origin  of  the  lymphatics. 

Adipose  tissue  consists  of  vesicles 
filled  with  fat  (figs.  77,  79)  and 
collected  into  lobules,  or  into  tracts 
which  accompany  the  small  blood- 
vessels. The  vesicles  are  round 
or  oval  in  shape,  except  where 
closely  packed,  when  the}^  become 
polyhedral  from  mutual  compres- 
sion. The  fat-drop  is  contained  with- 
in a  delicate  protoplasmic  envelope 
(fig.  77,  m)  which  is  thickened  at 
one  part,  and  here  includes  an  oval 
flattened  nucleus.  The  fat  is 
stained  black  by  osmic  acid ;  a 
deep  yellow  colour  by  Sudan  IIL  ; 
and  an  intense  red  by  Scharlach  R. 


Fig.  79. — Fat-cells  from  young  animal 

(Ranvier.)    Osmic  acid  preparation. 

Tlie    drops    of    fat    are    stained    of    an 

intense  black,     n,  nucleus  ;  g,  small 

globules  of  fat. 


74 


THE   ESSENTIALS   OF   HISTOLOGY. 


The  vesicles  are  supported  partly  by  filaments  of  areolar  tissue,  but 
chiefly  by  a  fine  network  of  capillary  bloodvessels. 

The  fat  when  first  formed  in  the  embryo  is  deposited  within  large 
granular  cells  of  areolar  tissue  (fig.  78)  similar  in  general  appearance  to 
the  "  Mast  "-cells  of  Ehrlich;  some  authorities  regard  them  as  of  a  specific 
nature,  for  they  are  in  certain  situations  collected  into  large  gland- 


Fig. 


-Two   STAGES    OF    FORMATION   OF   ADIPOSE   TISSUE.       (H.    Batty    Shaw. 


In  A  the  tissue  is  formed  of  a  gland-like  mass  of  cells,  in  some  of  which  the  cj'toplasm  is 
occupied  by  fat  globules  (looking  white  in  the  sections).  In  B  the  fat  fills  many  of 
the  cells. 

like  masses  (fig.  80)  abundantly  supplied  with  blood-vessels,  which 
gradually  become  transformed  into  fat-cells  by  the  deposition  of  fat  in 
the    cell-protoplasm.      Fat   is,    however,    also  laid  down   in   ordinary 


Fig.  81. — Retifoem  tissue  from  a  lymph-gland.     Moderately  magnified. 

tr,  a  trabeculum  of  connective  tissue  ;  r,  7-',  retiform  tissue,  with  more  open  meshes  at  >• 

and  denser  at  ■>•'. 

branched  cells  of  connective-tissue.  The  fat  appears  to  be  produced 
by  a  transformation  of  albuminous  granules  which  the  cells  con- 
tain into  droplets  of  fat.     As  the  droplets  increase  in  size  they  run 


adh'osk  tissue. 


7ri 


together  into  a  larger  drop,  which  gradually  fills  the  cell  more  and 
more,  swelling  it  out  so  that  the  cell-protoplasm  eventually  appears 
merely  as  the  envelope  of  the  fat-vesicle. 


Fig.  82. — Portion  of  the  .\bove,  more  highly  magnified, 

showing  the  continuity  of  the  retiform  tissue  >■,  r,  with  the  connective  tissue  of  a 
trabeculum,  ()•. 

Fat  is  found  most  abundantly  in  subcutaneous  areolar  tissue,  and 
under  the  serous  membranes ;  especially  in  some  parts,  as  at  the 
back  of  the   peritoneum  around  the  kidneys,  under  the  epicardium. 


Fig.  83.— Reticulum  of  bone-m.'^hkow.     (Enderlen.) 
and   in    the   mesentery   and   omentum.     The   yellow  marrow   of  the 
bones  is  also  princi[)ally  composed  of  fat.     There  is  no  adipose  tissue 
within  the  cavity  of  the  cranium. 

Eetiform  or  reticiilar  tissue  (figs.  81,  82,  83)  is  a  variety  of  con- 
nective tissue  in  which  the  intercellular  or  ground-substance  has  largely 


76 


THE   ESSENTIALS   OF   HISTOLOGY. 


disappeared  or  is  replaced  by  fluid.  There  are  very  few  or  no  elastic 
fibres  in  it,  but  a  dense  network  of  white  fibres,  the  meshes  of  which 
vary  in  size,  being  very  small  and  close  in  some  parts ;  more  open 
and  like  areolar  tissue  in  other  parts.  In  some  places  where  the 
tissue  occurs  the  fibres  are  enwrapped  by  flattened  branched  con- 
nective-tissue cells,  and  until  these  are  removed  it  is  not  easy  to  see 
the  fibres.  Chemical  diff'erences  between  the  fibres  of  retiform  tissue 
and  those  of  ordinary  areolar  tissue  have  been  described  by  Mall,  but 
microscopically  the  fibres  of  the  two  tissues  are  indistinguishable 
and  are  found  in  continuity  with  one  another  (see  figs.  82,  84).     This 


Fig.  84.— Lymphoid  tissue  of  a  lymph-gland. 


tissue  forms  a  fine  framework  in  many  organs,  supporting  the  proper 
elements  and  extending  into  all  the  interstices  between  the  coarser 
connective  tissue  bundles.  It  can  best  be  shown  by  dissolving  the 
cells  of  the  tissue  by  tryptic  digestion  and  subsequently  staining  the 
fibres  forming  the  reticulum  (p.  67,  §  5).  In  this  way  it  may  be  demon- 
strated in  lymph-glands,  in  the  spleen,  liver,  bone-marrow  (fig.  83), 
mucous  membranes,  and  many  other  parts. 

Lymphoid  or  adenoid  tissue  is  reticular  tissue  in  which  the  meshes 
of  the  network  are  largely  occupied  by  lymph-corpuscles  (fig.  84). 
This  is  by  far  the  most  common  condition  of  a  retiform  tissue,  and 


BA8KM  KNT-MEMBRANES.  77 

is  met  with  in  the  lyniph-i^huids  and  allied  structures,  and  also  in 
parts  of  the  alimentary  nuicous  membrane,  and  in  some  other 
situations. 

Basement-membranes  {me inb ranee  propriw)  are  homogeneous-looking 
membranes,  which  are  found  forming  the  surface  layers  of  connective- 
tissue  ex[)ansions  in  many  parts,  especially  where  there  is  a  covering 
of  epithelium,  as  on  mucous  membranes,  in  secreting  glands,  and  else- 
where. They  are  generally  formed  of  flattened  connective-tissue  cells 
joined  together  to  form  a  membrane;  but  in  some  cases  they  are 
evidently  formed  not  of  cells,  but  of  condensed  ground-substance,  and 
in  yet  other  cases  they  are  composed  of  elastic  substance ;  the  name 
basement-membrane  is  therefore  used  to  denote  structures  of  an 
entirely  different  nature. 

Jelly-like  connective  tissue,  although  occurring  largely  in  the 
embryo,  is  found  only  in  one  situation  in  the  adult — viz.  forming 
the  vitreous  humour  of  the  eye.  It  is  composed  mainly  of  soft, 
fluid,  ground-substance,  with  cells  scattered  here  and  there  through 
it,  and  with  a  few  fibres  which  interlace  throughout  the  tissue  and 
confine  the  fluid  of  the  ground-substance  within  their  meshes  ;  thus 
conferring  upon  the  tissue  its  jelly-like  character.  All  embryonic 
connective-tissue  is  in  the  first  instance  of  this  jelly-like  nature 
(see  p.  82). 


THE   ESSENTIALS  OF   HISTOLOGY. 


LESSON  X. 

THE  CONNECTIVE   TISSUES  {contimted). 

ELASTIC   TISSUE.      FIBROUS   TISSUE.      DEVELOPMENT    OF   CONNECTIVE 

TISSUE. 

1.  Tease  out  as  finely  as  possible  a  small  shred  of  elastic  tissue  (ligamentum 
nuclije  of  the  ox  or  ligamentum  subflavura  of  man)  in  glycerine  and  water, 
slightly  coloured  by  magenta.  Cover  and  cement  the  preparation.  Note 
the  large  well-defined  fibres  constantly  branching  and  uniting  with  one 
another.  Sketch  a  small  part  of  the  network.  Note  the  existence  of 
bundles  of  white  fibres  amongst  the  elastic  fibres. 

2.  Examine  a  thin  transverse  section  of  ligamentum  nnchge  which  has 
been  hardened  in  2  per  cent,  solution  of  bichromate  of  potash.  The  section 
is  to  be  stained  with  haemalum  and  mounted  in  Canada  balsam  or  dammar 
by  the  usual  process,  or  simply  in  glycerine  and  water.  Observe  the 
grouping  of  the  fibres  and  their  angular  shaj)e. 

3.  Pinch  ofi"  the  end  of  the  tail  of  a  dead  mouse  or  rat,  draw  out  the  long 
silk-like  tendons  and  put  them  into  salt  solution.  Take  one  of  the  threads, 
which  should  be  nearly  three  inches  long,  and  stretch  it  along  a  slide,  letting 
the  ends  dry  firndy  to  the  glass  but  keeping  the  middle  part  wet.  Put  a 
piece  of  hair  on  either  side  and  cover  in  salt  solution.  Observe  with  a  high 
power  the  fine  wavy  fibrillation  of  the  tendon.  Draw.  Now  run  dilute 
acetic  acid  (0'75  per  cent.)  under  the  cover-glass,  watch  the  tendon  where  it 
is  becoming  swollen  by  the  acetic  acid.  Notice  the  oblong  nucleated  cells 
comiug  into  view  between  the  tendon-bundles,  ^ketch  three  or  four  cells  in 
a  row.  Lastly,  lift  the  cover-glass,  wash  away  the  acid  with  distilled  water, 
place  a  drop  of  Ehrlieh's  hematoxylin  or  carmalum  solution  on  the  tendons, 
and  leave  the  preparation  until  it  is  deeply  stained  ;  then  wash  away  the 
stain  and  mount  the  preparation  in  faintly  acidulated  glycerine. 

4.  Take  another  long  piece  of  tendon,  and  after  washing  it  in  distilled 
water,  stretch  it  upon  a  slide  as  before,  fixing  the  ends  by  allowing  them  to 
dry  on  to  the  slide.  Put  a  drop  of  nitrate  of  silver  solution  (1  per  cent.) 
on  the  middle  of  the  tendon,  and  leave  it  on  for  five  minutes.  Then  wash 
off  the  silver  nitrate  with  distilled  water,  and  expose  the  slide  to  direct 
sunlight.  In  a  very  few  minutes  the  silvered  part  of  the  tendon  will  be 
brown.  As  soon  as  this  is  the  case,  dehydrate  the  tendon  with  absolute 
alcohol  in  situ  upon  the  slide,  run  ofi"  the  alcohol,  and  at  once  put  a  drop  of 
clove  oil  on  the  preparation.  In  a  minute  or  two  the  clove  oil  can  be 
replaced   by  xylol  balsam  or  dammar  and  the  preparation  covered. 

5.  Stain,  with  magenta  solution,  a  thin  section  of  a  tendon  which  has  been 
hardened  in  70  per  cent,  alcohol.  Mount  in  dilute  glycerine  and  cement 
at  once. 

6.  For  developing  connective  tissue  study  sections  of  the  umbilical  cord 
at  different  periods.  Fix  with  formol.  Stain  -with  acid  fuchsine  and 
haematoxylin. 


ELASTIC  TISSUE. 


79 


Elastic  tissue  is  a  variety  of  connective  tissue  in  which  the  elastic 
fibres  preponderate.  It  is  found  most  characteristically  in  the  liga- 
mentum  ruicha.'  of  quadrupeds  and  the  liganienta  subHava  of  the 
vertebrae,   but  the  connective  tissue  of  other  parts  may  also  have  a 


Fig.  85. — Ela.stic  fibres  from  the  ligamentum  nuch^e  of  the  ox, 
showing  transverse  markings  on  the  fibres. 

considerable  development  of  elastic  fibres.  It  occurs  in  an  almost 
pure  form  in  the  walls  of  the  air-tubes,  and  uniting  the  cartilages 
of  the  larynx.  It  also  enters  largely  into  the  formation  of  the  lungs 
and  of  the  walls  of  the  blood-vessels,  especially  the  arteries. 


I,. , 


Fig.  86.— Cross-section  of  elastic  fibres  from  the  ligamentum  NUCHiE 

OP  THE  ox. 

In  the  ligamentvim  nuchae  most  of  the  fibres  are  very  large  (figs. 
85,  86).  They  often  exhibit  cross  markings  or  even  transverse  clefts. 
When  dragged  asunder,  they  break  sharply  across.  They  constantly 
branch  and  unite,  so  as  to  form  a  close  network.  In  transverse  section 
they  are  seen  to  be  separated  into  small  groups  or  bundles  (fig.  86)  by 
intervening  septa  of  areolar  tissue. 


80  THE   ESSENTIALS   OF   HISTOLOGY. 

Elastic  tissue  does  not  always  take  the  form  of  fibres,  but  may 
occur  as  membranes  {e.g.  in  the  blood-vessels).  Sometimes  the  fibres 
are  very  small,  but  their  microscopic  and  chemical  characters  are 
always  very  marked  (see  p.  70). 


Fig.  87. — Section  of  tendon,  human.     (Sobotta.)   x  32. 
t,  tendon-bundles ;  s,  septa  of  areolar  tissue  ;  v,  vessels. 

Fibrous  tissue  is  almost  wholly  made  up  of  bundles  of  white  fibres 
running  in  a  determinate  direction.  These  again  are  collected  into 
larger  bundles,  w^hich  give  the  fibrous  appearance  to  the  tissue.  The 
bundles  are  constantly  uniting  with  one  another  in  their  course, 
although  their  component  fibres  remain  perfectly  distinct. 

The  interspaces  between  the  larger  bundles  are  occupied  by  areolar 


FiniJULTS   TISSUE. 


81 


tissue  (fig.  87,  fi ;  fig.  88,  c,  d,  e)  in  which  the  blood-vessels  and 
lymphatics  of  the  fibrous  tissue  are  conveyed.  The  interstices  between 
the  smallest  bundles  are  occupied  by  rows  of  lamellar  connective-tissue 


Fig.  88.— Part  of  a  large  tendon  in  transverse  section.     More  highly  magnified. 

a,  areolar  sheath  of  the  tendon,  with  the  fibres  for  the  most  part  running  transversely  ; 
but  with  two  or  three  longitudinal  bundles,  6  ;  I,  lymphatic  cleft  in  the  sheath ; 
Immediately  over  it  a  blood-vessel  is  seen  cut  across,  and  on  the  other  side  of  the 
figure  a  small  artery  is  shown  cut  longritudinally  ;  c,  large  septum  of  areolar  tissue  ; 
d,  smaller  septum  ;  e,  still  smaller  septum.  The  irregularly  stellate  bodies  are  the 
tendon-cells  in  section. 


A       £.- 


Fig.  89. — Tendon  of  mouse's  tail  (175  diameters) ;  showing  chains  ok 

CELLS  BETWEEN  THE   TENDON-BUNDLES. 
A,  stained  with  hsematoxylin.     B,  staineil  with  silver  nitrate,  showing  the  cell-spaces. 

F 


82  THE   ESSENTIALS   OF   HISTOLOGY. 

corpuscles  {tendon-rdh),  which,  from  being  squeezed  up  between  three 
or  more  bundles,  become  flattened  out  in  two  or  three  directions.  In 
transverse  section  the  cells  appear  somewhat  stellate  (fig.  88),  but 
when  seen  on  the  flat  they  appear  lamellar  (fig.  89),  and  from  this 
aspect  their  general  shape  is  square  or  oblong.  They  lie,  as  before 
said,  in  rows  between  the  tendon-bundles,  and  the  nuclei  of  adjacent 
cells  are  placed  opposite  one  another  in  pairs  (fig.  90).  The  cell-spaces 
correspond  in  general  figure  and  arrangement  to  the  cells  which  occupy 
them. 

Fibrous  tissue  forms  the  tendons  and  ligaments,  and  also  certain 
membranes,  such  as  the  dura  mater,  the  fibrous  pericardium,  the 
fasciae  of  the  limbs,  the  fibrous  covering  of  certain  organs,  etc.  It  is 
found  wherever  great  strength,  combined  with  flexibility,  is  concerned. 
It  receives  a  few  blood-vessels,  disposed  longitudinally  for  the  most 
part,  and  contains  many  lymphatics.  Both  blood-vessels  and  lymphatics 
run  in  the  areolar  tissue  which  separates  and  surrounds  the  tendon- 
bundles.     Tendons  and  ligaments  also  receive  nerve-fibres,  which,  in 


^lUg^^^gl^P^^^^P 


Fig.  90. — Eight  cells  i'ROM  the  same  tendon'  .\s  kepresented  in  fig.  89. 
(425  diameters.) 

The  dark  lines  on  the  surface  of  the  cells  are  the  optical  sections  of  lamellar  extensions 
directed  towards  or  away  from  the  observer. 

some  cases,  end  in  localised  ramifications  within  fusiform  enlargements 
of  the  tendon-bundles  (organs  of  Golgi),  while  others  terminate  in 
end-bulbs  or  in  simple  Pacinian  corpuscles.  These  will  be  described 
along  with  the  modes  of  ending  of  nerve-fibres. 

Development  of  connective  tissue. — Connective  tissue  is  developed 
in  and  from  the  cells  of  the  mesoderm  (mesenchyme)  of  the  embryo. 
In  those  parts  which  are  to  form  connective  tissue,  there  muy 
frequently  be  seen  a  clear  space  separating  the  cell-layers  which  are 
already  formed,  this  clear  space  being  permeated  with  fibres  which 
appear  to  be  produced  from  the  cells  bounding  the  space.  Presehtly 
branching  mesenchyme  cells,  which  are  derived  from  the  bounding  cell- 
layers,  are  found  forming  a  syncytium  within  the  clear  space  (fig.  91,  m). 
In  the  meshes  of  the  reticular  syncytium  is  a  muco-albuminous  semi- 
fluid intercellular  substance  (ground-substance).  The  connective-tissue 
fibres,  both  white  and  elastic,  are  deposited  in  this  ground-substance, 
the  elastic  substance  appearing  in  the  form  of  granules  (fig.  95,  g), 
which   subsequently  become  connected  together  into  elastic  fibres  or 


DEVELOPMENT  OF  CONNECTIVE  TISSUE. 


83 


^V 


''  «  ft 


Fig.  91.— Developing  connective  tissue  in  heart  of  chick-embuto  of 
48  HOURS.     (Szili.) 
my,  cells  forming  myocardium  ;  j,  jelly  formed  of  reticulum  with  enclosed  fluid  ;  <■,  endo- 
thelium (mesothelium)  of  heart ;  m,  mesenchyme  cells  in  jelly;  bl,  blood-corpuscles. 


K..:S^ 


^0 


\^^-"''''^^'^- 
X^'^^ 


X>^ 


Fig.  92.— Developing  connective  tissue  from  the  umbilical  cord  of 

A  HUMAN  EMBRYO  21  MM.  LONG.       (Minot. )       X  540. 


84 


THE   ESSENTIALS   OF   HISTOLOGY. 


0 


Al- 


i,    "^  ^      \     5^  "^t"^/^^  '^^  Wi^'' ''-■-••••■■"''''    ^"-\ 


Fig.  93.— Developing  connective  tissue  from  the  umbilical  cord  of  a 

THREE   MO.NTHS'   HUMAN   EMBRYO.       (Minot.)        X  511. 


> 


.--/ 


4 


#.  « 


4. 


Fig.  94. — Jelly  of  vvharton  from  umbilical  cord  of  new-born  child. 

(Sobotta.)     x280. 

/,  connective-tissue  fibres  ;  c,  cells. 


DEVELOPMENT  OF  CONNECTIVE   TISSUE. 


86 


laminae,  as  the  case  may  be,  the  white  fibres  appearing  at  first  in 
the  form  of  very  fine  bundles,  which  afterwards  become  gradually 
larger  (fig.  93) ;  so  that  in  fibrous  tissue  the  whole  ground-substance 
is  eventually  pervaded  by  the  bundles,  and  the  cells  of  the  tissue 
become  squeezed  up  into  the  intervals  between  them.  Before  any 
considerable  development  of  fibres  has  taken  place,  the  embryonic 
connective  tissue  has  a  jelly-like  appearance ;  in  this  form  it  occurs 
in  the  umbilical  cord,  where  it  is  known  as  the  jelly  of  Wharton 
(fig.  94). 

There  has  been  always  a  considerable  difference  of  opinion  as  to  the 
origin  of  the  fibres  of  connective  tissue,  some  histologists  holding  that 
they  are  formed  within  the  protoplasm  of  cells,  which  gradually  lose 


Fig.  9.5. — Development  of  elastic  tissue  by  deposition  of  fine  gkandles.. 

(Kanvier.) 

g,  fibres  being  formed  of  rows  of  '  elastin '  granules  ;  p,   flat  plate-like  expansion   of 
elastic  substance  formed  by  the  fusion  of  ' elastin'  granules. 


their  cell-characters  as  the  fibres  become  developed  within  them  ; 
others  taking  the  view  that  the  fibres,  both  white  and  elastic,  are 
extracellular  formations.  While  there  is  no  doubt  that  they  are 
produced  under  the  influence  of  the  cells,  for  they  first  appear  in 
close  proximity  to  those  structures,  it  seems  on  the  whole  probable 
that  the  fibres  are  deposited  in  the  ground-substance  and  not  actually 
in  the  cell-protoplasm,  so  that  they  are  rather  to  be  looked  upon,  like 
the  ground-substance  itself,  as  formed  by  a  process  of  secretion  than 
by  one  of  direct  cell-transformation. 


86  THE   ESSENTIALS  OF   HISTOLOGY. 


LESSON   XL 

THE  CONNECTIVE  TISSUES  {continued). 

ARTICULAR  CARTILAGE.      SYNOVIAL  MEMBRANES. 

1.  Cut  two  or  three  very  thin  tangential  slices  of  the  fresh  cartilage  of  a 
joint,  mount  them  in  .salt  solution,  and  examine  with  the  high  power. 
Observe  the  form  and  grouping  of  the  cells.  Look  at  the  thin  edge  of  the 
section  for  spaces  from  which  the  cells  have  dropped  out.  Measure  two  or 
three  cells  and  their  nuclei,  and  sketch  one  or  two  groups.  Now  replace 
the  salt  solution  by  water  and  set  the  preparation  aside  for  a  little  while. 
On  again  examining  it,  many  of  the  cartilage  cells  will  be  found  to  have 
retracted  away  from  their  containing  capsules. 

2.  Make  other  sections  of  the  cartilage  (1)  from  near  the  middle,  (2)  from 
near  the  edge.  Place  the  sections  for  two  or  three  minutes  in  acetic  acid 
(1  per  cent.),  wash  them  with  water,  and  stain  with  dilute  hjemalum  or 
carmalnm  solution.  When  stained  mount  in  dilute  glycerine  and  cement 
the  cover-glass.     In  (2)  look  for  branched  cartilage  cells. 

3.  Study  vertical  sections  of  articular  cartilage  from  an  end  of  bone 
which  has  been  fixed  and  decalcified,  and  mount  the  sections  in  glycerine 
and  water,  or,  after  staining  with  ha?malum,  in  dammar  or  xylol  balsam. 
Sketch  the  ai^rangement  of  the  cells  in  the  different  layers. 

4.  Brush  a  fresh  joint  with  distilled  water  ;  drop  1  per  cent,  nitrate  of 
silver  solution  over  it ;  after  five  minutes  wash  away  the  nitrate  of  silver 
and  expose  in  water  to  direct  sunlight.  When  browned,  place  in  spirit  for 
half  an  hour  or  more,  and  then  with  a  razor  wetted  with  spirit  cut  thin 
sections  from  the  surface  and  mount  in  xylol  balsam  or  dammar  after  passing 
through  clove  oil.  The  cells  and  cell-spaces  show  white  in  the  brown 
ground-substance. 

5.  To  study  the  structure  of  the  synovial  membrane  mount  other  slices 
from  the  silvered  preparation  of  the  joint  (§  4)  just  beyond  the  limits  of 
the  articular  cartilage,  and  also  look  for  small  fringed  projections  of  the 
membrane.     Snip  them  off  with  scissors  and  mount  as  before. 

6.  The  superficial  flexor  tendons  of  the  foot  of  the  ox  or  sheep  run  in 
grooves  formed  by  the  deep  flexors,  and  these  grooves  are  lined,  and  the 
tendons  which  pass  through  them  are  covered  by  vaginal  synovial  mem- 
branes. To  show  the  structure  of  these  treat  one  of  the  superficial  flexor 
tendons  with  silver  nitrate  in  the  manner  recommended  for  the  joint,  §  4, 
and  after  hardening  in  spirit  cut  sections  from  the  surface  and  mount  them 
in  balsam  or  dammar  varnish. 


Cartilage  or  gristle  is  a  translucent  bluish-white  tissue,  firm,  and  at 
the  same  time  elastic,  and  for  the  most  part  found  in  connection  with 
bones  of  the  skeleton,  most  of  which  are  in  the  embryo  at  first  repre- 
sented entirely  by  cartilage.     Three  chief  varieties   of  cartilage  are 


CARTILAGE. 


87 


distinguished.  In  one,  whicli  is  tei-med  liiialinc,  the  matrix  or  ground- 
substance  is  almost  clear,  and  free  from  obvious  fibres;  in  the  other 
two,  which  are  tcrined  Jihro-cartilage,  the  matrix  is  everywhere  pervaded 
by  connective-tissue  fibres.  When  these  are  of  the  white  variety,  the 
tissue  is  white  Jihro-cartiliuje ;  when  they  are  elastic  fibres,  it  is  yellow  or 
elastic  fihro-cariihuic 

Hyaline  cartilage  occurs  principally  in  two  situations — -namely  (1) 
covering  the  ends  of  the  bones  in  the  joints,  where  it  is  known  as 
articular  cartilage ;  and  (2)  forming  the  rib-cartilages,  where  it  is  known 


■#■ 


'^ 


f-^S' 


( (m 


^::nM0^''''^''^^-''''^^^^^^^^^-^ ' 


Fig.  96. — Articular  cartilage  from  head  of  metatarsal  bone  of  ampu- 
tated FOOT,  HUMAN  (OSMIC  ACID  PREPARATION).  THE  CELL-BODIES 
ENTIRELY    FILL  THE   SPACES    IN   THE   MATRIX.       (340   diameters.) 

a,  group  of  two  cells ;    b,   group   of   four  cells ;    h,  protoplasm   of  cell,    with  g,  fatty 
granules  ;  n,  nucleus. 


as  costal  cartilage.  It  also  forms  the  cartilages  of  the  nose,  of  the 
external  auditory  meatus  (but  not  the  pinna),  most  of  those  of  the 
larynx,  and  the  cartilages  of  the  windpipe ;  in  these  places  it  serves 
to  maintain  the  shape  and  patency  of  the  orifices  and  tubes. 

Articular  cartilage. — The  cells  of  articular  cartilage  are  generally 
scattered  in  groups  of  two  or  four  throughout  the  matrix  (fig,  96). 
The  latter  is  free  from  obvious  fibres,  except  at  the  extreme  edge 
of  the  cartilage,  where  the  connective-tissue  fibres  from  the  synovial 


88  THE   ESSENTIALS   OF   HISTOLOGY. 

membrane  extend  into  it ;  and  here  also  the  cartilage-cells  are  often 
branched,  and  offer  transitions  to  the  branched  connective-tissue 
corpuscles  of  that  membrane  {transitional  cartilage,  fig.  97).  By  long 
maceration  in  brine,  however,  evidence  of  a  fibrous  structure  may  be 


..'/ 


(v: 


Fig.  97.— Border  op  articulak  cartilage  showing  transition  of  cartil- 
age   CELLS   into   connective-tissue    CORPUSCLES    OF    SYNOVIAL    MEMBRANE. 

From  head  of  metatarsal  bone,  human.     (About  340  diameters.) 

a,  ordinary  cartilage-cells  ;  h,  h,  with  branching  processes. 

obtained,  even  in  the  matrix  of  true  hyaline  cartilage.  Some  his- 
tologists  also  describe  fine  communications  in  the  matrix  uniting  the 
cartilage-cells  with  one  another,  but  these  are  of  doubtful  occurrence  in 

vertebrate  cartilage,  although  they 
unquestionably  exist  in  the  cartilage 
of  cephalopods. 

The  matrix  immediately  around 
the  cartilage-cells  is  often  marked 
off  from  the  rest  by  a  concentric 
line  or  lines,  this  part  of  the  matrix, 
which  is  the  latest  formed,  being 
known  as  the  capsule  of  the  cell 
(fig.  98).  The  cells  are  bluntly 
angular  in  form,  the  sides  opposite 
to  one  another  in  the  groups  being 
generally  flattened.  The  proto- 
plasm is  very  clear,  but  it  may 
contain  droplets  of  fat;  and  with  a  high  power  fine  interlacing 
filaments  and  granules  have  been  observed  in  it.  During  life  the 
protoplasm  entirely  fills  the  cavity  or  cell-space  which  it  occupies  in 
the  matrix ;  but  after  death,  and  in  consequence  of  the  action  of  water 
and  other  agents,  it  tends  to  shrink  away  from  the  capsule.  The 
nucleus  is  round,  and  shows  the  usual  intranuclear  network. 


Fig.  98. — A  group  of  cartilage-cells 

SHOWING   THE   CAPSULAR  OUTLINES   IN 
THE  MATRIX  SURROUNDING  THE  GROUP. 

(Rauvier. ) 
«,  nucleolus  ;   h,  nucleus ;  c,  cytoplasm  of  a 
cell ;    d,    capsular    lines    in    pericellular 
matrix  ;  (,  fibrils  in  cartilage  matrix. 


ARTICULAR   CARTILAGE. 


8!> 


In  vertical  section  {tig.  Di))  the  deeper  cell  groups  (c)  are  seen  to  be 
arranged  vertically  to  the  surface,  the  more  superficial  ones  (a)  parallel 
to  the  surface ;  whilst  in  an  intermediate  zone  the  groups  are  irregu- 


r 


i     Gs     ©(Siea 


ii 


Fig.  99.— Vertical  section  of  articular  cartilace  (ovkkixc;  the  lower 
KND  OF  THE  TIBIA,  HUMAN.     (Magnified  about  30  diameters.) 

a,  cells  and  coil-groups  flattened  conformably  with  the  surface ;  b,  cell-groups  Irregu- 
larly arranged ;  c,  cell-groups  disposed  perpendicularly  to  the  surface ;  d,  layer 
of  calcified  cartilage  ;  e,  bone. 


Fig.  100.— Plan  of  the  multiplication  of  cells  op  cartilage.     (Sharpey.) 

A,  cell  in  its  capsule  ;  b,  divided  into  two,  each  with  a  capsule  ;  c,  primary  capsule 
disappeared,  secondary  capsules  coherent  with  matrix  ;  d,  tci'tiary  division ;  e, 
secondary  capsules  disappeared,  tertiary  coherent  with  matrix. 


larly  disposed  (h).  In  the  deepest  part  of  the  cartilage,  next  to  the 
bone,  there  is  often  a  deposit  of  calcareous  salts  in  the  matrix  (calcified 
cartilage,  d). 

The  disposition  of  the  cells  of  cartilage  in  groups  of  two,  four,  eight, 
etc.,  is  apparently  due  to  the  fact  that  these  groups  have  originated 


90 


THE    ESSENTIALS   OF   HISTOLOGY. 


from  the  division  of  a  single  cell  first  into  two,  and  these  again  into 
two,  and  so  on  (fig.  100).  The  division  of  the  cartilage-cell,  like  that 
of  most  other  cells,  is  mitotic. 

It  would  seem  that  the  matrix  is  formed  of  successive  portions, 
which  are  deposited  around  each  cartilage-cell  as  the  so-called 
'capsules,'  each  newly  formed  portion  soon  blending  in  its  turn  with 
the  previously  formed  matrix,  whilst  a  new  capsule  is  formed  within  it. 
The  most  newly  formed  portions  of  matrix  stain  with  haematoxylin 
more  deeply   than   the  rest,  and    in   some   cartilages    this    gives    the 

appearance  of  rounded  balls  of  darkly 
stained  matter  surrounding  each  cell  or 
cell-group  {clwivirin-haVs,  Morner). 

Embryonic  cartilage  is  characterised  by 
the  cells  being  usually  more  sharply  angular 
and  irregular ;  they  are  even  in  some  cases 
markedly  branched,  like  those  which  occur 
at  the  junction  of  cartilage  and  synovial 
membrane  in  the  adult.  The  cells  are 
also  more  closely  packed,  the  matrix  being 
in  relative!}'  less  amount  than  in  later  life. 
Development. — Cartilage  is  formed  in 
the  embryo  from  mesenchyme  similar  to 
that  which  gives  origin  to  other  forms 
of  connective-tissue.  Each  cell  forms  a 
capsule  around  itself,  and  the  blended 
capsules  compose  the  first  matrix.  Cartil- 
age sometimes  remains  in  this  condition 
throughout  life  ;  it  is  then  termed  paren- 
chymatous cartilage.  This  can  be  seen  in 
the  mouse's  ear  :  where  also  the  cartilage 
cells  become  filled  with  fat.  Cartilage 
grows  at  first  partly  by  interstitial  expan- 
sion (accompanied  by  cell  multiplication 
and  by  formation  around  and  between  the  cells  of  intercellular  sub- 
stance), partly  by  apposition  at  the  perichondrium,  the  connective 
tissue  becoming  here  transformed  into  cartilage.  At  a  later  period  of 
growth  the  increase  in  size  and  change  in  shape  of  cartilages  are  due 
almost  entirely  to  the  agency  of  the  perichondrium. 


Fig.  101. — Villus  OF  STXovi.\L 
MEMBRAXE.     (Hammar.) 


Synovial  Membranes. 
The   synovial   membranes    are    often    compared    with   the   serous 
membranes.       They    are    indeed,    like    the    latter,    connective-tissue 


SYNOVIAL   MEMBRANES.  91 

membranes  which  bound  closed  cavities  moistened  with  fluid,  but 
they  are  not  connected  with  the  lymphatic  system,  nor  is  the  fluid 
(synovia)  which  moistens  them  of  the  nature  of  lymph.  Moreover, 
there  is  either  no  endothelial  lining,  or  it  occurs  only  in  patches, 
in  place  of  the  continuous  lining  which  we  find  in  the  serous 
membranes.  Long  villus-like  projections  occur  in  many  parts ;  they 
are  often  covered  by  small  rounded  cells,  and  probably  serve  to 
extend  the  surface  for  the  secretion  of  synovia.  The  blood-vessels 
of  synovial  membranes  are  numerous,  and  approach  close  to  the  inner 
surface  of  the  membrane.  They  are  well  seen  in  preparations  from 
an  injected  limb. 


92  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    XII. 

THE   COS  SECT IV E   TISSUES   (continued). 

COSTAL   CARTILAGE.      FIBRO-CARTILAGE. 

L  Make  transverse  and  tangential  sections  of  a  rib-cartilage,  which  may 
either  be  fresh,  or  may  have  been  preserved  in  spirit  or  formol.  Stain  them 
with  hsenialum  or  carmalum  (if  fresh,  after  treatment  with  acetic  acid  as  in 
Lesson  XL  §  2,  or  they  may  be  placed  for  an  hour  or  two  in  "5  p.c.  osmic 
acid),  and  mount  in  glycerine.  Sketch  a  part  of  a  transverse  section  under 
a  low  power  and  a  cell-grou^i  from  one  of  the  tangential  sections  under  a 
high  power.  Notice  especially  the  arrangement  of  the  cells,  somewhat 
concentric  near  the  surface  but  radial  near  the  centre.  The  co.stal  cartilages 
tend  to  become  ossified  near  the  middle  in  most  animals,  but  in  man  when 
ossification  occurs  it  is  the  superficial  layer  which  is  invaded. 

2.  Make  sections  of  the  cartilage  of  the  external  ear  (pinna),  either  fresh 
or  after  hardening  in  alcohol.  Mount  in  dilute  glycerine  faintly  coloured 
with  magenta,  or  stain  with  orcein  and  mount  in  balsam.  If  from  the  ox, 
notice  the  very  large  reticulating  elastic  fibres  in  the  matrix.  Notice  also 
the  isolated  granules  of  elastin,  and  around  the  cartilage-cells  an  area  of 
clear  ground-substance.  If  from  the  mouse  or  rat  there  is  very  little  matrix 
and  no  elastic  fibres,  and  the  cells  are  almost  in  contact  (parenchymatous 
cartilage) ;  they  also  contain  fat  (staining  with  osmic  acid). 

3.  Mount  a  section  of  the  epiglottis  in  the  same  way.  Notice  the  closer 
network  of  much  finer  fibres  in  its  cartilage. 

4.  Cut  sections  of  white  fibro-cartilage  (intervertebral  disk  or  semilunar 
cartilage  of  knee),  which  has  been  hardened  in  picric  acid,  followed  by  spirit, 
or  in  spirit  only.  Stain  the  sections  with  dilute  htemalum  or  carmalum. 
Mount  in  dilute  glycerine.  Observe  the  wavy  fibres  in  the  matrix  and  the 
cartilage-cells  lying  in  clear  areas  often  concentrically  striated.  Look  for 
branched  cartilage-cells.  Sketch  three  or  four  cells  and  the  adjoining 
fibrous  matrix. 


Costal  cartilage.  —  In  the  costal  cartilages  the  matrix  is  not 
always  so  clear  as  in  the  cartilages  of  the  joints,  for  it  more  often 
happens  that  fibres  become  developed  in  it.  The  cells  are  generally 
larger  and  more  angular  than  those  of  articular  cartilage,  and 
collected  into  larger  groups  (fig.  102).  Xear  the  circumference, 
and  under  the  perichondrium  or  fibrous  covering  of  the  cartilage, 
they  are  flattened  and  parallel  to  the  surface,  but  in  the  deeper 
parts  they  have  a  more  irregular  or  a  radiated  arrangement.  They 
frequently  contain  fat.  The  cartilages  of  the  larynx  and  windpipe 
and  of  the  nose  resemble  on  the  whole  the  costal  cartilages,  but  the 


COSTAL  CARTILAGE.  93 

study  of  them   may   be  deterred   until   the  organs  where  they  occur 
-are  dealt  with. 

Elastic  or  yellow  fibre -cartilage  occurs  in  only  a  few  situations. 
These  are,  the  cartilage  of  the  external  ear  and  that  of  the  Eustachian 
tube,  and  the  epiglottis  and  cartilages  of  Santorini  of  the  larynx.  The 
matrix  is  everywhere  pervaded  with  well-defined  branching  fibres, 
which  unite  with  one  another  to  form  a  close  network  (figs.  103,  104). 
These  fibres  resist  the  action  of  acetic  acid,  and  are  stained  deeply 


;) 


■  ■^'>y-/i^ 


Fig.  102. — Sectiox  of  rib-cartilage,  showing  cells  and  cell-groups  ix 
ax  indistixctly  fibrous  matrix. 

Two  or  three  empty  cell-spaces  are   seen   from  which  the  cells  have  dropped  out  in 

preparing  the  section. 

by  magenta ;  they  are  evidently  elastic  fibres.  In  the  ox  they  are 
very  large,  but  smaller  in  man,  especially  in  the  cartilage  of  the 
epiglottis.  They  appear  to  be  developed,  as  with  elastic  tissue  else- 
where (see  p.  82),  by  the  deposition  of  gi'anules  of  elastin  in  the 
matrix,  which  at  first  lie  singly,  but  afterwards  become  joined  to  form 
the  fibres. 

White  fibro-cartilage  is  found  wherever  great  strength  combined 
with  a  certain  amount  of  rigidity  is  required  :  thus  we  frequently 
find  fibro-cartilage  joining  bones  together,  as  in  the  intervertebral 
disks  and  other  symphyses.  But  in  these  cases  the  part  in  contact 
with  the  bone  is  always  hyaline  cartilage,  which  passes  gradually 
into  ^the  fibro-cartilage  forming  the  bulk  of  the  symphysis.  Fibro- 
cartilage    is    often    found    lining    grooves    in    which    tendons    run, 


94 


THE   ESSENTIALS  OF   HISTOLOGY. 


4.> 


zap  ;  \-  ^ 


f 

Fig.  103. — Section  of  elastic  cartilage  of  ear,  hcmax.     (Sobotta.)     x2S0. 

c,  cartilage  cells ;   co.p,  their  capsules ;   in,  clear   matrix  around  ceUs  and   cell-groups  ; 

r",  elastic  fibres. 


mM 


Fig.  104.— Section  of  the  elastic  cartilage  of  the  ear. 
Highly  magnified. 


(R.  Hertwig.) 


Fig.  10.5.— "White  fibro-caetilage  from  an  intervertebral  disk,  human. 
Highly  magnified. 

The  concentric  lines  around  the  cells  indicate  the  limits  of  deposit  of  successive 
capsules.  One  of  the  cells  has  a  forked  process  which  extends  beyond  the  hyaline 
area  surrounding  the  cell,  amongst  the  fibres  of  the  general  matrix. 


FIBRO-CARTILAGE.  95 

and  it  may  be  found  in  the  tendons  themselves.  It  is  also  em- 
ployeil  to  deepen  cup-shaped  articular  surfaces ;  and  in  the  case  of 
the  interarticular  cartilages,  such  us  those  of  the  knee  and  lower  jaw, 
to  allow  greater  freedom  of  movement  whilst  diminishing  the  liability 
to  dislocation.  Under  the  microscope  white  fibro -cartilage  looks  very 
like  fibrous  tissue,  but  its  cells  are  cartilage-cells,  not  tendon-cells 
(fig.  105).  They  are  rounded  or  bluntly  angular  and  surrounded 
by  a  concentrically  striated  area  of  clear  cartilage-matrix.  In  some 
parts  of  the  intervertebral  disk  many  of  the  cells  are  branched, 
and  may  be  looked  upon  as  ti'ansitional  forms  to  connective-tissue 
corpuscles. 


m  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON   XIII. 
THE  C02sNECTIVE  TISSUES  {continued). 

BONE;    STEUCTITRE  AND  DEVELOPMENT. 

1.  Ix  thin  sections  of  hard  bone  made  by  grinding,^  observe  the  Haversian 
canals,  lamellae,  lacunae,  canaliculi,  etc.  Make  a  sketch  first  under  a  low  and 
afterwards  under  a  high  power. 

2.  With  fine  forceps  strip  off  a  thin  shred  from  the  superficial  layers  of  a 
bone  which  has  been  decalcified  in  5  p.c.  commercial  sulphurous  acid  and 
afterwards  washed  with  water  for  24  houi^s.  It  may  be  kept  in  dilute 
alcohol.  Mount  the  shred  in  water.  Observe  the  fibrous  structure  of  the 
lamella;.  Look  for  perforating  fibres  or  the  holes  from  which  they  have 
been  dragged  out.     Sketch  a  small  piece  of  the  thin  edge  of  a  lamella. 

3.  Stain  with  dilute  magenta  and  hremalum  solution,  or  with  methyl-blue 
and  eosin,  very  thin  sections  of  compact  bone  which  has  been  fixed  with 
10  p.c.  formol  (1  to  3  days)  and  then  decalcified  in  sulphurous  acid  as  above. 
Mount  in  dilute  glycerine,  cementing  at  once.  Look  for  fibres  of  Sharpey 
piercing  the  circumferential  lamellae.  The  elastic  perforating  fibres  are  more 
darkly  stained  than  the  others.  Notice  the  stained  nuclei  of  the  bone- 
corpuscles  in  the  lacunae.  In  the  thinne.st  parts  of  the  sections  try  to  make 
out  the  blood-vessels  and  other  structures  in  the  Haversian  canals. 

4.  Mount  in  xylol  balsam  or  dammar  a  section  of  a  fcetal  lower  jaw 
which  has  been  stained  in  bulk  and  embedded  in  paraffin.  Find  the  part 
where  the  lower  jaw-bone  is  becoming  ossified,  and  carefully  study  the 
appearance  which  it  presents.  The  bone  is  prolonged  in  the  form  of 
osteogenic  fibres  which  are  covered  with  osteoblasts. 

5.  Intramembranous  ossification  may  also  be  studied  in  the  parietal  bone 
of  a  foetus  which  has  been  preserved  in  Muller's  fiuid.  A  piece  of  the 
growing  edge  is  scraped  or  brushed  free  from  its  investing  membranes,  and 
from  most  of  the  cells  which  cover  and  conceal  it,  and  is  mounted  in 
glycerine  with  or  without  previous  staining  with  carmalum. 

6.  Mount  in  balsam  or  dammar  sections  of  a  fcetal  limb  (which  may  have 
been  stained  in  bulk).  The  bones  will  be  found  in  different  stages  of 
ossification,  those  of  the  digits  being  least  developed.  Make  sketches  illus- 
trating the  three  chief  stages  of  endochondral  ossification.  Notice  the 
peculiar  terminal  ossification  of  the  third  phalanx. 


Bone  i.s  a  connective  tissue  in  which  the  ground-substance  is 
impregnated  with  salts  of  lime,  chiefly  phosphate,  these  salts  consti- 
tuting about  two-thirds  of  the  weight  of  the  bone.  When  bones  are 
macerated  this  earthy  matter  prevents  the  putrefaction  of  the  animal 
matter.  When  bones  are  calcined  they  lose  one-third  of  their  weight, 
owing  to  the  destruction  of  the  animal  matter ;  when  steeped  in  acid 
^  It  is  best  to  purchase  these. 


BONE.  97 

the  earthy  salts  are  dissolved  and  only  the  animal  matter  is  left.    This, 
like  areolar  and  fibrous  tissue,  is  converted  into  gelatine  by  boiling. 


.>P''' 


Fig.  106.— Section  of  a  decalcified  human  radius.    (Sobotta.)     x48. 

periosteum  ;  pi,  periosteal  bony  lamellae  ;  p'V,  deeply  seated  lamellas  parallel  with 
periosteal  surface;  H,  Haversian  systems;  tr,  tr,  trabeculae  of  spongy  substance; 
rrd,  lamellae  bounding  medullary  spaces. 


Bony  tissue  is  either  compact  or  cancellated.  Compact  bone  is  dense, 
like  ivory ;  cancellated  is  spongy  with  obvious  interstices.  The  outer 
layers   of  all   bones   are   compact,   and   the   inner   part   is   generally 

G 


98 


THE   ESSENTIALS   OF   HISTOLOGY. 


cancellated,  but  the  shaft  of  a  long  bone  is  almost  entirely  made  up  of 
compact  substance,  except  along  the  centre,  which  is  hollow  and  filled 
with  marrow.  The  interstices  of  cancellated  bone  are  also  occupied 
by  marrow.  Externally  bones  are  covered  except  at  the  joints  by  a 
vascular  fibrous  membrane,  the  jjeriosteum. 

True  bone  is  always  made  up  of  lamellce,  and  these  again  are  com- 
posed of  fine  fibres  lying  in  a  calefied  fjround-mhstance.  Between  the 
lamellae  are  branched  cells,  the  bone-corpuscles,  which  lie  in  cell-spaces 
or  lacunm.  The  ramified  passages  which  contain  the  cell-processes  are 
termed  canaliculi. 


^l^iM'^ 


// 


^A^~x*'^yA ' ' 


Ui£jSk 


A- 


Fig.  107. 


-TRAN.SVERSE  SECTION  OF  COMPACT  TISSUE  (OF  HUMERUS). 

Magnified  about  1.50  diameters. 


(Sharpey.) 


Tliree  of  the  Haversian  canals  are  seen,  with  their  concentric  rings ;  also  the  lacunae, 
with  the  canaliculi  extending  from  them  across  the  direction  of  the  lamellae.  The 
Haversian  apertures  had  become  filled  with  air  and  debris  in  giinding  down  the 
section,  and  therefore  a]>pear  black  in  the  figure,  which  represents  the  object  as 
viewed  by  transmitted  light. 


In  cancellated  bone  the  blood-vessels  run  in  the  interstices  supported 
by  the  marrow.  In  compact  bone  they  are  contained  in  little  canals — 
the  Haversian  canals — which  everywhere  pervade  the  bone.  These 
canals  are  about  0-05  mm.  {-g^Q  inch)  in  diameter,  but  some  are 
smaller,  others  larger  than  this.  Their  general  direction  is  longi- 
tudinal, i.e.  parallel  to  the  long  axis  of  the  bone,  but  they  are 
constantly  united  by  transversely  and  obliquely  running  passages. 
In  a  section  across  the  shaft  of  a  long  bone  they  are  seen  as  small 
rounded  or  irregular  holes  (fig.  106).  When  the  section  has  been 
made  by  grinding,  the  holes  get  filled  up  with  air  and  debris,  and 
they  then   look  black  by  transmitted  light,   as   do   also  the   lacunae 


BONE. 


99 


and  canaliculi  (fig.  107).  Most  of  the  lamelhie  in  compact  bone  are 
disposed  concentrically  around  the  Haversian  canals ;  they  are  known 
as  the  Haversian  lamellw,  and  with  the  included  canal  form  what 
is  known  as  a  Haversian  system.  The  lacunae  of  a  Haversian  system 
communicate  with  one  another  and  with  the  Haversian  canal,  but 
not  as  a  rule  with  the  lacunae  of  adjacent  Haversian  systems.  The 
angular    interstices   between    the    Haversian    systems    are    generally 


Fig.  108.— Transverse  section  of  decalcified  human  tibia,  from  near  the 
surface  of  the  shaft. 

H,  H,  Haversian  canals,  with  their  systems  of  concentric  lamellas ;  in  all  the  rest  of  the 
figure  the  lamellae  are  circumferential ;  jt,  ordinary  perforating  fibres  of  Sharpey ; 
e,  e,  elastic  perforating  fibres.     Drawn  under  a  power  of  about  150  diameters. 


occupied  by  bony  substance  which  is  fibrous  but  not  lamellar. 
Besides  the  lamellae  of  the  Haversian  systems  there  is  a  certain 
thickness  of  bone  at  the  surface,  immediately  underneath  the 
periosteum,  which  is  composed  of  lamellae  arranged  parallel  with 
the  surface ;  these  are  the  circumferential  or  periosteal  lamelhe  (fig. 
106,  pi).  They  are  pierced  here  and  there  by  simple  canals  for 
blood-vessels,  the  so-called  Volhnann's  canals,  which  are  proceeding 
from  the  periosteum  to  join  the  system  of  Haversian  canals,  and 
also  by  calcified  bundles  of  white  fibres  and  by  elastic  fibres  which 
may  also  be  prolonged  from  the  periosteum.  These  are  the  per 
forating  fibres  of  Sharpey  (fig.  108). 


100  THE   ESSENTIALS  OF  HISTOLOGY. 

The  lamellfe  of  bone  are  fibrous  in  structure.  This  may  be  seen  in 
shreds  torn  off  from  the  superficial  layers  of  a  decalcified  bone 
(fig.  109).  The  fibres  {decussating  fibres  of  Sharpey)  often  cross  one 
another  in  adjacent  lamellae,  and  in  the  Haversian  systems  they  run 
in  some  lamellae  concentrically,  in  others  parallel  with  the  Haversian 
canal.  In  shreds  of  lamellae  which  have  been  peeled  off"  from  the 
surface  the  perforating  fibres  ma}^  sometimes  be  seen  projecting  from 
the  surface  of  the  shred,  having  been  torn  out  of  the  deeper  lamellae 


Fig.  109.— Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at 

SOME  DEPTH  FROM  THE  SURFACE.   (Sbarpej'.) 

a,  lamellie,  showing  decussating  fibi-es  ;  b,  i,  thicker  part,  where  several  lamellae  are 
superposed  ;  c,  c,  jierforating  fibres ;  the  fibrils  which  compose  them  are  not  shown 
in  the  figure.  Apertures  through  which  perforating  fibres  had  passed  are  seen, 
especially  in  the  lower  part,  a,  of  the  figure.  Magnitude  as  seen  under  a  power  of 
200  diameters,  but  not  drawn  to  scale.     (From  a  sketch  by  Allen  Thomson.) 

(fig.  109,  c,  c).  When  tendons  or  ligaments  are  inserted  into  bone, 
their  bundles  of  white  fibres  are  prolonged  into  the  bone  as  perforating 
fibres. 

The  lacunae  are  occupied  by  nucleated  corpuscles,  which  send 
branches  along  the  canaliculi  (fig.  110).  They  have  a  special  lining 
layer  different  in  chemical  composition  from  the  rest  of  the  bone,  being 
much  more  resistant  to  the  action  of  strong  chemical  solvents  such  as 
hydrochloric  acid  (Neumann).  The  dentinal  tubules  of  the  teeth  have 
a  similar  lining  layer. 

The  Haversian  canals  contain  one  or  two  blood-capillaries  and 
nervous  filaments,  besides  a  little  connective  tissue ;  and  the  larger  ones 
may  also  contain  a  few  marrow-cells.  There  are  also  cleft-like  lym- 
phatic spaces  running  with  the  vessels,   their  cells  being  connected 


BONE. 


101 


through  canaliculi  with  branches  from  corpuscles   within    the    neigh- 
bouring lacunae  of  the  osseous  substance  (fig.  111). 

The  periosteum  may  be  studied  in  torn-off  shreds,  in  preparations 
stained  in  situ  Avith  silver  nitrate,  and  in  stained  sections  from  an 
unmacerated  bone  which  has  been  decalcified.  It  is  a  fibrous 
membrane  composed  of  two  layers,  the  inner  of  which  contains 
many   elastic   fibres.      In    the    outer    layer    numerous   blood-vessels 


Fig.  110.— a  bone-cell  isol-^ted 
and  highly  magnified. 
(Joseph. ) 
a,    proper   wall    of    the    lacuna    (Neu- 
mann's layer),  where   the   corpuscle 
has  shrunken  away  from  it. 


Fig.  111.— Section  of  a  haversian  canal, 

SHOWING    ITS    CONTENTS.       (Highly 

magnified.) 
a,  small  arterial  capillary  vessel ;  v,  large  venous 
capillary ;  71,  pale  nerve-fibres  cut  across ; 
I,  cleft-like  lymphatic  vessel;  one  of  the  cells 
forming  its  wall  communicates  by  fine  bi-anches 
with  the  branches  of  a  bone-corpuscle.  The 
substa,nce  in  which  the  vessels  run  is  connec- 
tive tissue  with  ramified  cells ;  its  finely 
gi-anular  appearance  is  probably  due  to  the 
cross-section  of  fibrils.  The  canal  is  sur- 
rounded by  several  concentric  lamellaj. 

ramify  and  send  branches  to  the  Haversian  canals  of  the  bone.  The 
periosteum  ministers  to  the  nutrition  of  the  bone,  partly  on  account 
of  the  blood-vessels  and  lymphatics  it  contains,  partly,  especially  in 
young  animals,  on  account  of  the  existence  between  it  and  the 
bone  of  a  layer  of  osteoblasts  or  bone-foj-ming  cells,  a  remainder  of 
those  which  originally  produced  the  bone.  It  also  serves  to  give 
attachment  to  muscular  fibres. 

The  marrow  of  bone  has  been  already  studied  (pp.  38,  39). 


DEVELOPMENT  OF  BONE. 

True  bone  is  essentially  formed  in  all  cases  by  an  ossification  of 
connective  tissue.  Sometimes  the  bone  is  preceded  by  cartilage,  which 
first  becomes  calcified,  and  this  is  then  invaded,  and  for  the  most  part 
removed,  by  an  embryonic  tissue  which  re-deposits  bony  matter  in  the 
interior  of  the  cartilage.  This  is  intracartilaginous  or  endochondral  ossi- 
fiadion.     At  the  same  time  layers  of  bone  are  being  formed  outside  the 


102 


THE   ESSENTIALS   OF   HISTOLOGY. 


cartilage  underneath  the  periosteum.  The  whole  bone  thus  formed  is 
termed  a  cartilage-hone.  Sometimes  the  bone  is  not  preceded  by  carti- 
lage, and  then  the  only  process  which  occurs  is  one  corresponding  to  the 
subperiosteal  ossification  of  the  cartilage-bone  ;  the  ossification  is  then 
known  as  intramemhranous,  and   the  bone  formed  is  a   membrane-bone. 


Fig.  112.— Section  of  phalangeal  bonk  of  hdman  fcetus  at  the  time  of 
COMMENCING  OSSIFICATION.  (From  a  prepaiation  bj-  F.  A.  Dixey.)  The 
preparation  was  stained  in  bulk  with  magenta.  The  drawing  is  made  from 
a  photograph,  and  is  magnified  about  75  diameters. 

The  cartilage  cells  in  the  centre  are  enlarged  and  separated  from  one  another  by  stained 
calcified  matrix  ;  im,  layer  of  bone  deposited  underneath  the  periosteum  ;  o,  layer  of 
osteoblasts  by  which  the  layer  has  been  formed.  Some  of  the  osteoblasts  are  already 
embedded  in  the  new  bone  as  lacun*.  The  cartilage-cells  ai-e  becoming  enlarged  and 
flattened  and  arranged  in  rows  above  and  below  the  calcified  centre.  At  the  ends  of 
the  cartilage  the  cells  are  small,  and  the  groups  are  irregularly  arranged  ;  the  fibrous 
periosteum  is  not  sharply  marked  off  from  the  cartilage. 

Ossification  of  cartilage.— This  may  be  described  as  occurring  in 
three  stages.  In  the  _^rs;  stage  the  cells  in  the  middle  of  the  cartilage 
become   enlarged   and   arranged  in   rows   radiating   from    the    centre 


OSSIFICATION   OF  CARTILAGE. 


103 


(fig.  112),  and  fine  granules  of  calcareous  matter  are  deposited  in  the 
matrix.  Simultaneously  with  this  the  osteoblasts  underneath  the 
periosteum  deposit  a  layer  or  layers  of  fibrous  lamella?  upon  the 
surface  of  the  cartilage,  and  these  lamellae  also  become  calcified 
(fig.  112,  im).  As  they  are  formed,  some  of  the  osteoblasts  (o)  are 
included  l)etween  them  and  become  bone-corpuscles. 


Fig.  113.— Section  of  part  of 
one  of  the  limb-bones  of 
a  fcetal  cat,  at  a  more 
advanced  stage  of  ossifi- 
cation than  is  represented 
in  fig.  112,  and  somewhat 
more  highly  magnified. 
Drawn  from  a  photograph. 

The  calcification  of  the  cartilage- 
matrix  has  advanced  from  the 
centre,  and  is  extending  between 
the  groups  of  cartilage-cells,  which 
arc  arranged  in  characteristic 
rows.  The  subperiosteal  bony 
deposit  (im)  has  extended  pari 
passu  with  the  calcification  of  the 
cartilage-matrix.  The  cartilage 
cells  in  the  calcified  part  are 
mostly  shrunken  and  stellate ;  in 
some  cases  they  have  dropped  out 
of  the  spaces.  At  ir  and  in  two 
other  places  an  irruption  of  the 
subperiosteal  tissue,  composed  of 
ramified  cells  with  osteoblasts 
and  growing  blood-vessels,  has 
penetrated  the  subperiosteal  bony 
crust,  and  has  begun  to  excavate 
secondary  areolaj  or  medullary 
spaces ;  p,  fibrous  layer  of  the 
periosteum  ;  o,  layer  of  osteo- 
blasts, some  of  them  are  em- 
bedded in  the  osseous  layer  as 
bone-corpuscles  in  lacuna;.  The 
blood-vessels  are  occupied  by  blood- 
corpuscles.  Beyond  the  line  of 
ossific  advance  the  periosteum 
may  be  noticed  to  be  distinctly 
incurved.  This  incurvation  is 
gradually  moved  on,  the  carti- 
lage expanding  behind  it  until 
the  head  of  the  bone  is  reached, 
when  it  forms  the  periosteal 
notch  or  groove  represented  in 
figs.  116  and  119. 


In  the  second  stage  some  of  the  subperiosteal  tissue  eats  its  way 
through  the  newly  formed  layer  of  bone  and  into  the  centre  of  the 
calcified  cartilage  (fig.  113,  ir).  This  is  freely  absorbed  before  it 
(fig.  115),  so  that  large  spaces  are  produced  which  are  filled  with 
osteoblasts,  and  contain  numerous  blood-vessels  which  have  grown 
in  at  the  same  time.  These  spaces  are  termed  medullary  spaces,  and 
this  second  stage  may  be  termed  the  stage  of  irruption. 


104 


THE   ESSENTIALS  OF   HISTOLOGY. 


In  the  third  stage  of  endochondral  ossification  there  is  a  gradual 
advance  of  the  ossification  towards  the  extremities  of  the  cartilage,  and 
at  the  same  time  a  gradual  deposition  of  fresh  bony  lamellse  and  spicules 
on  the  walls  of  the  medullary  spaces,  and  on  the  surface  of  the  new 
bone  under  the  periosteum.  The  advance  into  the  cartilage  always 
takes  place  by  a  repetition  of  the  same  changes,  the  cartilage-cells  first 
enlarging  and  becoming  arranged  in   rows,   the  matrix  between  the 


Fig.  114. — Part  of  a  longi- 
tudinal SECTION  OF  THE 
DEVELOPING     FEMDR      OF      THB 

RABBIT.  (Klein.)  (Drawn  un- 
der a  magnifying  power  of  350 
diameters. ) 

a,  rows  of  flattened  cartilage-cells  ; 

b,  gieatly  enlarged  cartilage-cells 
close  to  the  advancing  bone,  the 
matrix  between  is  partly  calcified ; 

c,  d,  already  formed  bone,  the 
osseous  trabeculte  being  covered 
with  osteoblasts  (()  except  here  and 
there,  where  an  osteoclast  (/)  is 
seen  eroding  parts  of  the  trabe- 
culfe  ;  g,  h,  cartilage-cells  which 
have  become  shrunken  and  irre- 
gular in  shape.  From  the  middle 
of  the  figure  downwards  the 
trabecular,  which  are  formed  of 
calcified  cartilage-matrix,  are  be- 
coming covered  with  secondary 
osseous  substance  deposited  by 
the  osteoblasts.  The  vascular 
loops  at  the  extreme  limit  of  the 
bone  are  well  shown,  as  well  as 
the  abrupt  disappearance  of  the 
cartilage-cells. 


rows  becoming  calcified,  and  then  the  calcified  cartilage  becoming 
excavated  from  behind  by  the  osteoblastic  tissue  so  as  to  form  new 
medullary  spaces  (fig.  114).  The  walls  of  these  are  at  first  formed  only 
by  remains  of  the  calcified  cartilage-matrix  (fig.  114,  c),  but  they  soon 
become  thickened  by  lamellae  of  fibrous  bone  which  are  deposited  by 
the  osteoblasts,  and  between  which  bone-corpuscles  become  included, 
as  in  the  case  of  the  subperiosteal  bone.  The  latter  advances  pan  passu 
with  the  endochondral  calcification,   but  beyond  this  the  uncalcified 


OSSIFICATION   OF  CARTILAGE. 


105 


cartilage  grows  both  in  length  and  breadth,  so  that  the  ossification 
is  always  advancing  into  larger  portions  of  cartilage ;  hence  the 
endochondral  bone  as  it  forms  assumes  the  shape  of  an  hour-glass,  the 
cylindrical  shape  of  the  whole  bone  being  maintained  by  additions  of 
periosteal  bone  to  the  outside  (see  fig.  116).  The  absorption  of  the 
calcified  cartilage-matrix  appears  to  be  effected,  as  is  the  case  with 
absorption  of  bony  matter  wherever  it  occurs,  by  large  multi-nucleated 


Fig.  115.— Longitudinal  section  through  part  of  a  phalanx  of  a  six 
months'  human  embryo.     (Kolliker. ) 

The  calcified  cartilage  is  completely  absorbed  almost  to  the  limit  of  advancing  calcifica- 
tion. The  osseous  substance  on  either  side  is  periosteal  bone.  The  embryonic 
marrow  has  shrunk  somewhat  away  from  it. 

cells  (fig.  11-i, /, /)  which  are  termed  osteoclasts.  They  are  cells  of  the 
same  nature  as  the  myeloplaxes  of  the  marrow,  and  are  found 
on  surfaces  where  absorption  of  bone  is  taking  place,  whereas  the 
osteoblasts  are  always  found  covering  surfaces  where  bony  deposit 
is  proceeding  (fig.  117). 

The  bone  which  is  first  formed  is  more  reticular  and  less  regularly 
lamellar  than  that  of  the  adult,  and  contains  no  Haversian  systems. 


106 


THE   ESSENTIALS   OF   HISTOLOGY. 


The   regular   lamellae   are   not   deposited  until  some  little  time  after 
birth,   and   their   deposition  is  generally  preceded  by  a  considerable 


Fig.  110.— Longitudinal  sec- 
tion THROUGH  THE  UPPER  HALF 
OF  THE  DECALCIFIED  HUMERUS 
OF  A  FCETAL  SHEEP,  AS  SEEN 
UNDER  A  M.\GNIFY1NG  POWER 
OF  ABOUT  30  DIAMETERS. 


,  the  part  of  the  shaft  which  was 
primarily  ossified  in  cartilage ; 
what  remains  of  the  primary  bone 
is  represented  dark,  enveloped  by 
the  clear  secondary  deposit.  The 
areolae  of  the  bone  are  occupied  by 
embryonic  marrow  with  osteo- 
blasts, and  blood-vessels  variously 
cut.  One  long  straight  vessel  (pv) 
passes  in  advance  of  the  line 
of  ossification  far  into  the  cartil- 
aginous head,  most  of  the  others 
loop  round  close  to  the  cartilage. 
At  one  or  two  places  in  the 
older  parts  of  the  bone  elongated 
groups  of  cartilage-cells  (er)  may 
still  be  seen,  which  have  hitherto 
escaped  absorption,  m,  the  part 
of  the  bone  that  has  been  ossified 
in  membrane,  that  is  to  say,  in 
tlie  osteoblastic  tissue  under  the 
periosteum.  It  is  well  marked 
off  from  the  central  portion,  and 
is  bounded,  peripherally,  by  a 
jagged  edge,  the  projections  of 
which  are  indistinctly  seen  to  be 
prolonged  by  bunches  of  osteo- 
genic fibres.  A  row  of  osteoblasts 
covei-s  the  superficial  layer  of  the 
bone.  The  subperiosteal  layer  is 
prolonged  above  into  the  thicken- 
ing {p)  which  encroaches  upon 
the  cartilage  of  the  head  of  the 
bone,  and  in  which  are  seen 
amongst  numerous  osteoblasts  and 
a  few  blood-vessels,  the  straight 
longitudinal  osteogenic  fibres  («/'), 
and  some  other  fibres  (pf)  crossing 
them,  and  perhaps  representing 
fibres  of  Sharpey.  The  calcareous 
salts  having  been  removed  by  an 
acid,  the  granular  ossific  deposit 
passing  up  between  the  rows  of 
cartilage-cells  is  not  seen  in  this 
specimen  ;  it  would  have  extended 
as  far  as  a  line  joining  the  marks 
X  X.  ObseiTe  the  general  ten- 
dency of  the  osseous  trabeculse 
and  the  vascular  channels  between 
them  to  radiate  from  the  original 
centre  of  ossification.  This  is 
found  to  prevail  more  or  less  in 
all  bones  when  they  are  first 
formed,  although  the  direction  of 
the  ti-abeculie  may  afterwards  be- 
come modified  in  relation  with 
varying  physiological  conditions, 
and  especially  as  the  result  of 
pressure  in  different  directions. 


amount  of  absorption.  It  is  about  this  time  also  that  the  medullary 
canal  of  the  long  bones  is  formed  by  the  absorption  of  the  bony 
tissue  which  originally  occupies  the  centre  of  the  shaft. 


OSSIFICATION   OF  CARTILAGE. 


107 


\\ 


\ 


After  a  time  the  cartilage  in  one  or  both  ends  of  the  long  bones 
begins  to  ossify  independently,  and 
the  epiphi/se.^  are  formed.  These 
are  not  joined  to  the  shaft  until  the 
growth  of  the  bone  is  completed. 
Cxrowth  takes  place  in  lemjth  by  an 
expansion  of  the  cartilage  {inter- 
mediate cartilage)  which  intervenes 
between  the  shaft  and  the  epiphj^ses, 
and  by  the  gradual  extension  of 
the  ossification  into  it ;  in  midth 
entirely  by  the  deposition  of  fresh 
bony  layers  under  the  periosteum. 
In  the  terminal  phalanges  of  the 
digits  the  ossification  starts, 
from  the  middle  of  the  cartilage,  but 
from  its  distal  extremity  (Dixey). 

For  the  regeneration  of  portions 
of  bone  which  [have  been  removed 
by  disease  or  operation  it  is  important  that  the  periosteum  be  left 


Y 


not    Fig.  117.— Boxy  trabecul,e  from  the 

DEVELOPING  LOWER  J.\W  OF  A  CALF, 
SHOWING  OSTEOCLASTS  .\T  THE  EX- 
TREMITIES WHERE  ABSORPTION  IS  PRO- 
CEEDING, AND  OSTEOBLASTS  COVERING 
THE  SIDES  WHERE  DEPOSITION  OF  BONE 

IS  GOING  ON.     (Kolliker. ) 


Fig.  118.— Transverse  section  of  a  developing 
bone,  showing  the  periosteal  layer  becom- 
ing formed  from  osteogenic  fibres. 

cb,  cartilage  bone  ;  pb,  periosteal  bono  ;  sp,  bone  spicules 
prolonged  by  osteogenic  fibres  ;  p,  periosteum  ;  hi, 
blood-vessels  ;  c,  remains  of  the  calcified  cartilage  ; 
o,  osteoblasts  forming  bone  upon  this. 


Fig.  119.— Section  of  the  ossi- 
fication    GROOVE     IN     THE 

HEAD   OF   A   LONG    BONE. 

c,  cartilage ;  p,  periosteal  tissue 
with  osteogenic  fibres  and  osteo- 
blasts. This  tissue  occupies  the 
"groove." 


108 


THE   ESSENTIALS   OF   HISTOLOGY. 


Intramembranous  ossification. — In  this  A-ariety  of  ossification  (fig. 
120),  the  bone  is  not  preceded  by  cartilage  at  all,  and  therefore  no 
endochondral  bone  is  formed,  but  the  calcification  occurs  in  a  sort 
of  embryonic  fibrous  tissue  which  contains  numerous  osteoblasts  and 
blood-vessels.  The  fibres  of  this  tissue  (osteogenic  fibres),  which, 
like  those  of  fibrous  tissue,  are  collected  into  small  bundles,  become 
inclosed  in  a  calcareous  matrix,  produced  by  the  deposition  of  lime 
salts  in  the  ground-substance  of  the  connective  tissue  :  and  as  the 
fibres  grow,  the  calcification  extends  further  and  further,  so  that  bony 


Fig.  120.— Part  of  the  growing  edge  of  the  developixg  parietal  boxe  of 
A  fcetal  cat,  1|  inch  long. 

sp,  bony  spicules,  with  some  of  the  osteoblasts  embedded  iu  them,  producing  the 
lacunM  ;  of,  osteogenic  fibres  prolonging  the  spicules,  with  osteoblasts  {pit)  between 
them  and  applied  to  them  ;  a,  granular  calcific  deposit  occurring  in  the  ground- 
substance  between  the  fibres  ;  c,  union  of  two  adjacent  spicules. 

spicules  are  formed,  which,  as  they  become  thickened,  run  together 
to  form  reticular  layers,  leaving  spaces  filled  with  osteoblasts  around 
the  blood-vessels.  The  osteogenic  fibres  are  covered  with  osteoblasts, 
and  as  the  bone  forms,  some  of  these  become  left  as  bone-corpuscles 
within  lacunae.  Thus  in  every  particular  the  development  of  these 
bones  resembles  that  of  the  subperiosteal  laj-er  of  endochondral  bone ; 
which  is  also  to  be  considered  as  an  instance  of  intramembranous 
ossification,  although  taking  place  on  the  surface  of  cartilage.  More- 
over, it  is  the  same  subperiosteal  tissue  which,  in  endochondral 
ossification,  deposits  the  true  or  secondary  bone  upon  those  parts  of 


OSSIFICATION   IN   ^lEMBRANE.  109 

the  calcified  cartilage-matrix  which  have  escaped  absorption;  and  this 
must  also,  therefore,  be  reckoned  as  developed  according  to  the  same 
type.  In  fact,  even  in  intracartilaginous  ossification,  very  little  of  the 
calcified  cartilage-matrix  eventually  remains  ;  this  being  almost  wholly 
absorbed  and  either  replaced  by  true  or  fibrous  bone  which  has  been 
formed  by  osteoblasts,  or  swept  away  to  form  the  medullary  and 
other  cavities. 

"With  reference  to  the  origin  of  the  osteoblasts,  it  has  been  thought  by 
some  authors  that  they  are  derived  from  the  blood-vessels,  and  are  in  fact 
leucocytes  whicli  have  wandered  out  of  the  vessels  and  have  taken  on  the 
special  osteogenic  function.  Another  and  a  more  proljable  view  regards 
theru  as  niodi6ed  connective  tissue  cells  formed  within  the  periosteum  and 
merely  accompanying  the  vessels  into  the  interior  of  the  ossifying  cartilages. 
They  have  also  been  thought  to  be  formed  by  division  and  alteration  of  the 
cartilacre-cells. 


110  THE   ESSENTIALS  OF   HISTOLOGY. 


LESSON   XIV. 

STRUCTURE  OF  STRIATED   MUSCLE. 

1.  Take  a  shred  of  muscle  from  a  recently  killed  mammal,  and  on  a  dry  slide 
carefully  sepai'ate  long  pieces  of  muscular  fibres  (single  fibres  if  possible)  and 
stretch  them  out,  keejjing  them  moist  during  the  process  by  breathing  on 
the  slide.  Put  a  drop  of  serum  on  the  cover-glass  before  placing  this  over 
the  preparation.  Study  first  with  a  low,  then  with  a  high  power.  Sketch 
all  the  apj)earances  to  be  seen  in  a  small  piece  of  a  fibre,  focussing  carefully 
the  most  superficial  layers.  Notice  the  oval  nuclei  immediately  under  the 
sarcolemiua.  Then  allow  a  little  dilute  acetic  acid  to  run  under  the  cover- 
glass  and  watch  its  effect. 

2.  Prepare  some  fibres  of  frog's  nmscle  in  the  same  way,  but  mount  in 
salt  solution  instead  of  serum.  Notice  the  muscular  substance  shrinking 
away  here  and  there  from  the  sarcolemma,  which  then  becomes  distinctly 
visible.  Sketch  a  piece  of  sarcolemma  bridging  across  an  interval  thus 
produced. 

3.  Study  transverse  sections  of  muscle  which  has  been  hardened  in  alcohol 
or  formol  and  stained.  Mount  in  dammar  varnish  or  xylol  bals^am.  Examine 
the  section  of  a  fibre  first  with  a  low  and  then  with  a  high  power.  Sketch 
the  appearances  which  are  seen. 

In  each  of  the  above  preparations  measure  the  diameter  of  some  of  the 
fibres. 

Sections  of  muscle-spindles  may  be  searched  for  in  the  transverse  sections 
of  muscle. 

4.  Place  in  1  per  cent,  osmic  acid  a  small  shred  of  mammalian  muscular 
tissue  which  has  been  stretched  upon  a  cork.  After  '24  hours,  when  it  will 
be  deeply  stained,  wash  it  in  water  and  with  needles  break  the  fibres  up  in 
glycerine  as  finely  as  possible.     Cover  and  examine  with  a  high  power. 

5.  Cut  off  the  head  of  a  small  garden  beetle  or  wasp,  and  bisect  the  trunk 
with  scissors  so  as  to  expose  the  interior.  Notice  two  kinds  of  muscular 
tissue,  the  one  belonging  to  the  legs  greyish  in  colour,  the  other  attached  to 
the  wings  yellowish.  Preparations  of  both  kinds  of  muscle  are  to  be  made 
in  the  same  way  as  living  mammalian  muscle  (i$  1),  but  it  is  better  to  mount 
them  in  a  drop  of  white  of  egg.  In  both  jn-eparations  the  dark-looking 
air-tubes  or  tra<-he:e  form  prominent  objects  ramifying  amongst  the  fibres. 
Observe  the  structure  of  the  two  kinds  of  muscle  so  far  as  it  can  be  made 
out  in  the  fresh  ])reparation.  If  the  preparation  is  made  quickly,  waves  of 
contraction  will  probably  be  observed  passing  along  the  fibres. 

6.  Make  another  preparation  of  the  leg-muscles,  mounting  the  muscle  in 
vinegar.  (Alcohol-hardened  muscle  of  insect  or  crab  may  be  used  for  this 
purpose.)  Notice  that  the  muscular  substance  swells  up  somewhat  and 
becomes  clearer,  whilst  the  sarcoplasm-network,  with  its  lines  and  dots, 
comes  more  distinctly  into  view.  In  a  well-teased  preparation  of  alcohol- 
hardened  muscle,  the  fibres  will  be  frequently  found  breaking  across  into 
disks.     Make  careful  drawings  from  this  preparation. 

7.  Rollett's  method.  Cut  off"  the  head  of  an  insect  (wasp,  small  beetle), 
bisect  the  trunk  and-  place  in  90  per  cent,  alcohol  for  from  24  to  48  hours 


STRUCTURE   OF   STRIATED   MUSCLE. 


Ill 


or  more.  Then  take  a  small  piece  of  each  kind  of  muscle,  and  place  in 
strong  glycerine  for  some  hours.  Wash  thoroughly  with  water  and 
transfer  to  I  per  cent,  chloride  of  gold  solution  :  leave  the  pieces  of  muscle 
in  this  from  lo  to  30  minutes  according  to  their  size.  From  the  gold 
solution  tliey  are  transferred  to  formic  acid  (1  part  of  the  strong  acid  to 
3  of  water),  and  kept  in  the  dark  for  24  hours,  but  they  may  be  kept  longer 
without  disadvantage.  The  muscle  is  then  teased  in  glycerine.  Some  of 
the  fibres  will  be  found  after  this  method  to  have  their  sarcoplasm  darkly 
stained,  and  to  show,  therefore,  the  appearance  of  a  network  both  in  longi- 
tudinal and  transverse  view  :  others,  on  the  other  hand,  liave  the  sarcous 
elements  of  the  fibrils  or  sarcostyles  stained,  whilst  the  sarcoplasm  has 
remained  colourless. 


Voluntary  muscle  is  composed  of  long  cylindrical  fibres,  measuring 
on  an  average  about  0-05  mm.  in  diameter  (^i^y  inch)  in  mammalian 


Fig.  121. 


Fig.  123. 


Fig.  121. — S.\rcolemma  of  mammalian  muscle  highly  magnified. 
The  fibre  is  represented  at  a  place  whei-e  the  muscular  s\ibstauce  has  become  ruptured 
and  has  shrunk  away,  leaving  the  sarcoleninia  (with  a  nucleus  adhering  to  it)  clear. 
The  fibi-e  had  been  treated  with  serum  acidulated  with  acetic  acid. 

Fig.  122. — Muscular  fibre  of  a  mammal  examined  fresh  in  serum,  highly 

magnified,  the  surface  op  the  fibre  being  accurately  focussed. 
The  nuclei  are  seen  on  the  flat  at  the  surface  of  the  fibre,  and  in  profile  towards  the  edge. 

Fig.  123.— Portion  of  a  medium-sized  human  muscular  fibre,  showing  the 

INTERMEDIATE  LINE  (DOBIE's  LINE)  MENTIONED  IN  THE  TEXT.       (Sliarpey.) 

muscles,  and  often  having  a  length  of  an  inch  or  more.  Each  fibre 
has  an  elastic  sheath,  the  sarcolemma,  which  incloses  the  contractile 
substance.  The  sarcolemma  is  seldom  distinct,  unless  the  contained 
substance  becomes  broken  (fig.  121). 


112 


THE   ESSENTIALS  OF   HISTOLOGY. 


The  contractile  substance  of  the  fibre  is  characterised  by  the  alter- 
nate dark  and  light  stripes  which  run  across  the  length  of  the  fibre ; 
hence  the  name,  cross-striated  or  striped  muscle.  On  focussing,  it  can  be 
seen  that  the  stripes  pass  through  the  whole  thickness  of  the  fibre ; 
they  may  therefore  be  looked  upon  as  representing  alternate  disks  of 
dark  and  light  substance.  If  the  fibre  be  very  carefully  focussed,  rows 
of  apparent  granules  are  seen  lying  in  or  at  the  boundaries  of  the  light 
streaks,  and  very  fine  longitudinal  lines  may,  with  a  good  microscope, 
be  detected  uniting  the  apparent  granules  (fig.  122).  These  fine  lines, 
with  their  enlarged  extremities  the  granules,   are    more  conspicuous 


Fig.  124. — S.mall  portion  of  .\ 
mdscle  fibre  of  cr.\b  split- 
TING   UP    INTO    FIBRILS.       (FlODl   a 

photogra])li. ) 

Magnified  600  diameters. 


Fig.  125. — Section  of  a  muscdlar 
fibre,  showing  areas  of  cohn- 

HEIM. 
Three  nuclei  are  seen  lying  close  to  the 
sarcolemma. 


in  the  muscles  of  insects.  They  indicate  the  divisions  between  the 
longitudinal  elements  {fibrils  or  sarcosti/k.<)  which  compose  the  fibre, 
and  in  preparations  treated  with  dilute  acid  they  appear  to  form  part 
of  a  fine  network,  which  pervades  that  substance,  and  serves  to  unite 
the  granules  both  transverseh"  and  longitudinally.  This  network, 
which  is  sometimes  very  distinct  in  preimrations  of  muscle  treated 
with  chloride  of  gold,  is,  however,  a  network  in  appearance  only  :  in 
reality  it  is  the  optical  expression  of  the  interstitial  substance  which 
lies  between  the  fibrils.     This  substance  is  termed  sarcoplasm. 

On  examining  the  transverse  section  of  a  fibre  with  a  high  power, 
it  is  seen  to  be  subdivided  everywhere  into  small  angular  fields, 
Cohnheim's  areas  (fig.  125),  which  are  themselves  again  divided  up. 
The  smallest  divisions  represent  sections  of  the  fibrils  of  which  the 
fibres  are  composed,  and  into  which  they  may  be  split  after  death, 
especially  after  being  hardened  in  certain  reagents,  e.g.  chromic  acid 


VOLUNTARY  MUSCLE.  113 

or  osmic  acid.  The  larger  areas  represent  groups  of  fibrils.  These 
areas  of  Cohiiheim  are  usually  polyhedral,  but  they  may  be  elongated, 
and  disposed  either  radially,  or  concentrically  with  the  circumference 
of  the  section.  The  interstitial  substance  or  sarcoplasm  lies  between 
them  and  can  l)e  made  visible  by  treatment  with  dilute  acid  or  by 
staining  with  chloride  of  gold  (figs.  127,  128,  and  129).  It  is  some- 
times in  relatively  large  amount,  but  in  most  muscular  fibres  is 
I'educed  to  a  very  fine  interstitium. 

An  ill-defined  clear  line  is  sometimes  seen  running  trans versel}'' 
across  the  fibre  in  the  middle  of  each  dark  band.  This  is  termed 
Hcnsen's  line. 

If  instead  of  focussing  the  surface  of  the  fibre  it  be  observed  in  its 
depth,  an  appearance  different  from  that  shown  in  fig.  122  is  frequently 
visible,  namely,  a  fine  dotted  line  {Dobie's  line),  bisecting  each  clear 
stripe  (fig.  123);  this  appearance  is  often  considered  to  represent  a 
membrane  {Krause's  membrane),  which  subdivides  the  fibrils  at  regular 
intervals  (see  p.  116).  But  the  membrane  of  the  individual  fibrils  or 
.sarcostyles  is  rarel}^,  if  ever,  visible  in  an  intact  mammalian  fibre,  and 
it  is  certain  that  the  appearance  of  such  a  line  in  the  middle  of  the 
clear  stripe  of  an  intact  fibre  is  in  most  cases  due  to  interference, 
caused  by  the  light  being  transmitted  between  disks  of  diff"erent 
refrangibility. 

Haycraft  ha.s  suggested  that  the  cross-striation  of  voluntary  muscle  is 
due  to  refractive  effects  produced  by  a  varicosity  of  the  component  fibrils, 
basing  his  view  upon  the  fact  that  in  impressions  of  the  fibres  made  in  soft 
collodion  all  the  cross-striations  which  are  observed  in  the  fibre  itself  are 
reproduced.  Theie  is  no  doubt  that  a  well-marked  cross-striated  appearance 
can  be  produced  in  homogeneous  fibrils  by  regularly-occurring  varicosities, 
and  many  of  the  appearances  observed  in  muscle  may,  as  Haycraft  contends, 
be  referred  to  this  cause.  But  even  when  a  fibre  or  fibril  is  stretched  so 
that  it  exhibits  no  varicosities,  the  cross-striations  are  still  perfectly  distinct. 
Moreover,  in  view  of  the  entirely  different  manner  in  which  the  substance 
of  the  dark  and  clear  stripes  behave  to  many  staining  reagents,  and  especially 
to  chloride  of  gold  when  applied  as  directed  in  §  7,  the  fact  being  that  very 
definite  structural  appearances  can  under  these  circumstances  be  made  out, 
the  homogeneity  of  the  muscle-fibinl  cannot  be  admitted.  This  inference  is 
strongly  confirmed  by  the  microchemical  work  of  A.  B.  Macallum,  who  has 
shown  that  the  j^otassium  salts  of  the  muscle  are  mainly  accumulated  in  the 
sarcous  elements. 

Nuclei. — Besides  the  sarcolemma  and  striated  substance,  a  muscular 
fibre  also  exhibits  a  number  of  oval  nuclei  which  have  the  usual 
structure  of  cell-nuclei:  their  chromatin  often  has  a  spiral  aixangement. 
Sometimes  there  is  a  little  graimlar  substance  (protoplasm)  at  each 
pole  of  the  nucleus ;  each  nucleus  with  the  adjacent  protoplasm  has 
then  been  spoken  of  as  a  inuscle-corpusde.  But  the  protoplasm  which 
is  adjacent  to  the   nuclei  is  in  all  probability  continuous   with   the 


114 


THE   ESSENTIALS   OF   HISTOLOGY. 


sarcoplasm  between  the  fibrils  ;  both  being  the  remains  of  the  original 
undifferentiated  protoplasm  of  the  cells  from  which  the  muscular  fibres 
are  developed.      In  mammalian  muscle  the   nuclei   usually  lie  imme- 


FiG.  126.— Living  muscle  of  water-beetle 
(dttiscus  marginalis.)     (Highly  maguified.) 

s,  sarcoloiuma  ;  a,  dim  stripe  ;  h,  bright  stripe ;  c,  row 
of  dots  in  ijright  stripe,  which  seem  to  be  the 
enlai-ged  ends  of  rod-shaped  paiticles,  d,  but  are 
really  expansions  of  the  interstitial  sarcoplasm 
which  appear  in  the  living  muscles  as  fine  dark 
lines  with  dot-like  enlargements  upon  them. 


Fk;.  127. — Portion  of  leg-muscle 
OF  insect  treated  with  dilute 

ACID. 
S,  sarcolemma  ;  V.  dot-like  enlargement 
of  sarcoplasm  ;  K,  Krause's  membrane. 
The  sarcous  elements  are  dissolved  or 
at  least  rendered  invisible  by  the  acid. 


liiiir 


.Jim  iiiiii 

llpiSH  liliiliiiiiJiB) 


^iffiTm\ 


\\^' 


Fig.  128. 


Fig.  129. 


Fig  128. — Transverse  section  of  leg-muscle  fibre  of  an  insect, 
stained  with  gold  chloride 
The  sarcoplasm  is  here  stained,  and  appears  in  the  foroi  of  a  network,  in  the  meshes  of 
■which  He  the  sections  of  the  fibrils.  Xotice  the  mottled  appearance  of  the  sections 
of  the  sarcostylcs  or  fibrils,  indicating  a  porous  structure,  as  in  the  wing  fibrils 
(see  fig.  132).  The  central  protoplasm  (with  a  nucleus)  is  also  evident.  (From  a 
photograph.) 

Fig  129. — Leg-muscle  fibre  of  insect  treated  with  dilute  acid,  showing 

a  tendency  to  break  across  into  disks. 
The  sarcoplasm  is  in  the  form  of  fine  lines.     The  ordinary  dark  stripes  of  the  fibre  have 

disapi>eared  in  the  acid.     A,  a  disk  seen  partly  in  section  and  exhibiting  the  reticular 

an-angement  of  the  sarcoplasm  ;  B,  longitudinal  view  of  fibre. 


VOLUNTARY  MUSCLE.  115 

diately  under  the  sarcolemma  (figs.  121,  122,  125),  in  frog's  muscle 
they  are  scattered  throughout  the  sul)stance  of  the  fibre  ;  in  insect 
muscle  they  occupy  the  middle  of  the  fibre,  embedded  in  graiuilar 
protoplasm  (fig.  128).  Some  animals,  such  as  the  rabbit,  have,  besides 
muscles  of  the  ordinary  type  of  structure,  which  in  this  animal  are  pale 
in  colour,  others  of  a  deep  red  colour.  These  red  muscles  were  found  by 
Kanvier  to  exhibit  certain  differences  both  in  structure  and  function. 
One  difference  of  structure  is  that  the  nuclei,  which  are  numerous,  are 
not  confined  to  the  surface,  but  are  scattered  throughout  the  substance 
of  the  fibres.  The  fibres  in  question  also  contain  more  sarcoplasm 
than  the  ordinary  fibres,  and  their  blood- 

vessels   have   a   peculiarity    of  structure  % 

which  will  be  afterwards  noticed.     Here  !    ,^._  | 

and  there,  in  all  mammals,  amongst  the  )••••:'>•• = .-.^ — K 

ordinary   fibres   are   some  in   which   the         '  „  j 

nuclei  are  distributed  through  the  thick-         !    .  ;  ..i^-^- 

ness  of  the  fibres;  this  is  the  case  also,         \iniTi . . , . . ; ..' 

as  just  remarked,  with  all  the  muscular         ["['"'^^"['"""""^X 
fibres  of  the  fros;.     In  muscles  which  are         !     , 


in    constant    activity,    such    as   the   dia-         s   '"i":       i  :    r,    -^ 

phragm    and   the   dorsal    fin   muscles   of 

TT-                             ,1                ^      1              /  Fig.   130.— Leg-muscle  fibre  of 

Hippocampus,     the     protoplasm     (sarco-  insect,    st-^ined    with    gold 

plasm)   of  the   fibres  is  present  in  rela-  chloride  by  rollett's  method. 

,       ,                                 .                   ,  ,   .       .         ,  A',    line    formed    by    membranes    of 

tively    large   proportion,    and  this    is    also  Kiause;    S.E.,   dark   stripe   formed 

,                              •.■I        ^1              ■  -I              n  by    sarcous    elements.     The    sarco- 

the      case      with      the      wing  muscles      OI  pksm  has  the  appearance  of  longi- 

,  tudinal  lines. 

insects. 

The  transverse  section  of  a  muscle  shows  the  fibres  to  be  nearl}'' 
cylindrical  in  figure.  Between  the  fibres  there  is  a  certain  amount  of 
areolar  tissue,  which  serves  to  support  the  blood-vessels  and  also 
unites  the  fibres  into  fasciculi ;  the  fasciculi  are  again  united  together 
by  a  larger  amount  of  this  intramuscular  connective  tissue  (endo- 
mysium.) 

Ordinary  or  leg-muscles  of  insects. — In  the  muscles  of  insects  the 
stripes  are  relatively  broad,  and  their  structure  can  be  more  readily 
seen  than  in  mammals.  In  the  living  fibres  from  the  muscles  which 
move  the  legs,  the  sarcoplasm  presents  a  striking  appearance  of  fine 
longitudinal  lines  traversing  the  muscle,  and  enlarging  within  the 
light  stripes  into  rows  of  dots  (fig.  126).  This  is  still  better  seen  in 
fibres  and  portions  of  fibres  which  have  been  treated  with  dilute  acid 
(fig.  127).  In  separated  disks  produced  by  the  breaking  across  of 
muscle-fibres,  the  surfaces  of  the  disks  show  a  network  with  poly 
hedral  meshes  in  some  insects  (fig.  129,  a),  one  formed  of  lines  radiating 


116  THE   ESSENTIALS   OF   HISTOLOGY. 

from  the  centre  of  the  fibre  in  others.  The  nuclei,  with  some  inclosing 
protoplasm,  lie  in  the  middle  of  the  fibre. 

Wing-muscles  of  insects. — The  wing-muscles  of  insects  are  easily 
broken  up  into  fibrils  (sarcostyles),  which  also  show  alternate  dark 
and  light  striiB  (fig.   131). 

The  sarcostyles  are  subdivided  at  regular  intervals  by  thin  transverse 
disks   {membranes  of  Krause)   into  successive  portions,   which  may  be 


Fig.  131. — Fibrils  of  the  wi.ng-muscles  of  a  wasp,  PREPAREn  by  kollet's 
METHOD.     Highly  magnified.     (From  photographs.) 

A,  a  contracted  fibril.  B,  a  stretched  fibril,  with  its  sarcous  elements  separated  at 
the  line  of  Hensen.  C,  an  uncouti-acted  fibril,  showing  the  porous  structure  of 
the  sarcous  elements. 

termed  sarcomeres.  Each  sarcomere  is  occupied  by  a  portion  of  the 
dark  stria  of  the  whole  fibre  (sarcous  element) :  the  sarcous  element 
is  really  double,  and  in  the  stretched  fibre  separates  into  two  at  the 
line  of  Hensen  (fig.  131,  b).  At  either  end  of  the  sarcous  element  is 
a  clear  substance  (probably  fluid  or  semi-fluid)  separating  it  from  the 
membrane  of  Krause :  this  clear  substance  is  more  evident  the  more 
the  fibril  is  extended,  but  diminishes,  even  to  complete  disappearance, 
in  the  contracted  muscle  (fig.  131,  a).     The  cause  of  this  change  is 


WING-MUSCLES  OF   INSF.CTS. 


ir 


explained  when  we  study  more  minutely  the  structure  of  the  sarcous 
element.  For  we  find  that  each  sarcous  element  is  pervaded  with 
longitudinal  canals  or  pores,  which  are  open  in  the  direction  of  Krause's 
membranes,  but  closed  at  the  middle  of  the  sarcous  element  (fig.  132). 
In  the  contracted  muscle,  the  clear  part  of  the  muscle-substance  has 
disappeared  from  view,  but  the  sarcous  element  is  swollen  and  the 
sarcomere  is  thus  shortened:  in  the  uncontracted  muscle,  on  the  other 
hand,  the  clear  part  occupies  a  considerable  interval  between  the 
sarcous  element  and  the   membrane  of  Krause,  the  sarcomere   being 


/  I 


Fig.  132. — Isolated  sarcous  elements 
OP    A    wing-muscle,    showing    the 

TUBULAR   OR   POROUS   STRUCTURE. 

(Magnified  2300  diameters.) 
Some  are  seen  in  profile  ;  others  on  the  flat. 


S.E.- 


Fig.  133. — Diagram  of  a  sarcomere  in  a 
moderately  extended  condition,  a, 
and  in  a  contracted  condition,  b. 

K,  K,  membranes  of  Krause  ;  H,  line  or  plane  of 
Hensen  ;  S.B.,  poriferous  sarcous  element. 


lengthened  and  narrowed.  The  sarcous  element  does  not  lie  free 
in  the  middle  of  the  sarcomere,  but  is  attached  at  either  end  to 
Krause's  membrane  by  very  fine  lines,  which  may  represent  fine  septa, 
running  through  the  clear  substance  (fig.  133);  on  the  other  hand, 
Krause's  membrane  appears  to  be  attached  laterally  to  a  fine  membrane 
which  limits  the  fibril  externally. 

The  planes  of  sarcous  elements  set  side  by  side  in  a  muscle-fibre 
form  the  dark  stripe  (the  so-called  principal  disk)  of  the  muscle- 
substance  of  ordinary  muscle-fibres  (fig.  130).  But  in  the  wing-muscles 
of  insects  the  sarcous  elements  of  the  fibrils  less  constantly  lie  in 
continuous  planes,  and  the  whole  fibre  is  therefore  very  indistinctly 
and  irregularly  cross-striated,  although  each  individual  fibril  is  markedly 
so  (fig.  131).  As  already  stated,  the  sarcous  elements  are  remarkable 
for  containing  a  large  proportion  of  potassium  salts  (Macallum). 

Sometimes  in  the  ordiiiar\'  (leg)  muscles  of  arthropods  what  look  like 
detached  dot-like  portions  of  the  sarcous  element  are  seen  within  the  clear 
stripes,  lying  usually  near  Krause's  membrane.  The  rows  of  such  dots  liave 
been  termed  accessor^/  disks.  Most  muscles  show  no  accessory  disks,  but  the 
sarcoplasmic  enlargements  between  the  fibrils  (fig.  127,  d)  are  often  mistaken 
for  them. 


118 


THE   ESSENTIALS   OF   HISTOLOGY. 


Muscle  in  polarised  light. — When  muscle-fibres  are  examined  with 
polarised  liglit  between  crossed  Nichol's  prisms,  the  sarcous  elements  (which 
form  the  dark  stripe)  are  seen  to  be  doubly  refracting  (anisotropous),  while 
the  clear  substance  (forming  the  light  stripe)  is  singly  refracting  (isotropous). 
In  contracted  parts  of  the  muscle  the  (anisotropous)  sarcous  elements  are 
seen  to  have  increased  in  bulk,  while  the  isotropous  substance  of  the  clear 
stripe  has  correspondingly  diminished  in  amount  (fig.  134,  b). 


Fig  134— Leg-muscle  fibre  of  chbysomela  coerulea  with  (fixed)   con- 
traction  WAVE   photographed   UNDER    POLARISING   MICROSCOPE.l 

A,  with  uncrossed  Nichols  ;  B,  with  crossed  Xichols, 


F.  Merkel  described  a  reversal  of  the  stripes  during  contraction,  i.e.  a 
transference  of  the  anisotropous  substance  of  the  dark  stripe  from  Hensen's 
line  to  Krause's  membrane,  the  place  of  the  dark  stripes  thus  becoming 
occupied  by  clear  material,  that  of  the  light  stripes  by  dark.  He  further 
described  this  condition  as  being  preceded  by  an  intermediate  stage  in  which 
the  fibril  shows  homogeneity  of  shading.  No  doubt  in  the  ordinary  muscle- 
fibres  of  arthrojjods,  when  we  observe  the  so-called  '  fixed '  waves  of  con- 
traction, there  is  an  apparent  blurring  of  the  cross-striation  of  the  fibre  just 
where  the  muscle  is  passing  from  extension  to  contraction,  but  this  appear- 
ance is  explicable  by  the  unequal  pull  of  the  contracted  parts  of  the  fibrils 
upon  those  which  are  not  yet  contracted.  The  contraction  in  each  fibre 
starts  from  the  nerve-ending,  which  is  at  one  side  of  the  fibre,  and  spreads 
first  across  the  fibre  and  then  tends  to  pass  as  a  wave  towards  either  end. 
But  the  one  side  always  has  a  start  in  the  progress  of  this  wave,  and  the 
fibrils  must  thus  receive  an  unequal  pull,  so  that  they  are  shifted  along  one 
another  and  the  liue  of  cross-striping  is  broken  up.  That  no  transference  of 
anisotropous  substance  really  occurs  is  at  once  clear  from  the  appearance 

1 1  am  indebted  to  Professor  Engelmann  for  these  two  photographs. 


MUSCLK    IN   POLARISED   LIGHT. 


119 


of  the  contracting  fibre  under  jjolaiised  linht  (fi,t^.  134,  h),  nnd  the  study  of 

the  isolated  (ibrils  of  winy;-niuscle  gives  no  support  to  the  tlieory  of  reversal, 

although  it  is  widely  held  by  (xerinan  authors.     That  the  apparent  reversal 

is    not  real  is  also   illustrated    by 

fig.    135,    which    represents    a    leg 

muscle  fibre  of  an  insect  in  process 

of  contraction.     The  dark  bands  of 

the    ct)ntraction-wave   are    seen    to 

be  really  due  to  accumulations  of 

sarcoplasm.      These   accumulations 

appear  as  dark  lines  which  obscure 

the  continuity  of   the  fibrils,  and 

by  contrast  cause  the  whole  of  the 

sarcomeres  between  them  to  aiipear 

light. 

"Mechanism  of  contraction. — 
Comparing  the  structure  of  the  sar- 
comere with  that  of  the  protoplasm 
of  an  amteboid  cell  we  find  in  both 
a  framework  (spongiopiasm,  sub-' 
stance  of  sarcous  element)  which 
incloses  in  its  meshes  or  pores  a 
clear,  probably  fluid  substance 
(hyaloplasm,  clear  substance  of 
sarcomere).  In  both  instances  also 
the  clear  substance  or  hyaloplasm, 
when  the  tissue  is  subjected  to 
stimulation,  passes  into  the  pores 
of  the  porous  substance  or  spongio- 
piasm (contraction),  whilst  in  the 
ab.sence  of  such  stimulation  it  tends 
to  pass  out  from  the  spongiopiasm 
(formation  of  pseudopodia,  resting 
condition  of  muscle).  The  effect 
of  stimulation  appears  in  both 
structures  to  be  the  production  of  a 
change  in  surface  tension  (perhaps 
between  the  hyaloplasm  and  spon- 
giopiasm) ;  this  change  being  de- 
monstrably accompanied  in  muscle 
by  a  ditference  in  electric  jJotential. 
In  all  probability  such  an  electric 
change  occurs  in  all  protoplasm.  Thus  both  the  movements  of  cell-protoplasm 
and  those  of  muscle  seem  brought  about  by  like  means,  although  at  first 
sight  the  structure  of  muscle  is  cjuite  dissimilar  from  that  of  protoplasm. 

We  have  already  noticed  that  the  movements  of  cilia  are  susceptible  of  a 
somewhat  similar  explanation. 


Fig.  13.5. — "Wave  of  contraction  passing 
over  a  leg-muscle  fibre  of  dytiscus. 
Highly  magnified. 


120  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    XV. 

CONNEXION  OF  MUSCLE  WITH  TENDON;  BLOOD-VESSELS  OF 
MUSCLE;  CARDIAC  MUSCULAR  TISSUE;  DEVELOPMENT  OF 
MUSCLE;   PLAIN  MUSCULAR  TISSUE. 

1.  To  study  the  connexion  of  muscle  with  tendon,  a  frog  is  killed  by  destruc- 
tion of  the  brain  and  spinal  cord,  and  placed  in  about  a  litre  of  water  raised 
to  a  temperature  of  55°  C.  It  is  left  in  this  for  15  minutes,  the  water 
gradually  cooling.  It  is  then  easy  to  dissociate  the  muscular  fibres  in  large 
numbers.  To  obserA^e  their  attachment  to  the  tendon-bundles  a  fine  longi- 
tudinal shred  must  be  snipped  off  with  scissors  at  the  tendinous  attachment^ 
and  dissociated  upon  a  slide  in  a  drop  of  water.  It  will  usually  be  found 
that  the  muscular  substance  is  retracted  from  the  end  of  the  sarcolemma 
tube,  which  is  firmly  cemented  to  the  tendon-bundle.  The  structure  may  be 
brought  more  distinctly  into  view  by  adding  to  the  dissociated  fibres  a  drop 
of  a  weak  solution  of  iodine  in  salt  solution  or  iu  serum  (iodised  serum).' 

2.  The  blood-vessels  of  muscle.  These  are  studied  in  longitudinal  and 
transverse  sections  or  in  flattened-out  pieces  of  injected  muscle.  It  will  be 
noticed  that  the  capillaries  are  very  numerous,  and  form  a  network  with 
oblong  meshes.  In  the  red  muscles  of  the  rabbit,  small  dilatations  are  seen 
on  the  transverse  cords  of  the  network. 

3.  The  muscular  tissue  of  the  heart  is  studied  in  sections  of  that  organ 
(see  Lesson  XXVII.)  and  also  in  teased  preparations.  To  prepare  the  latter, 
place  a  small  piece  of  heart-muscle  in  33  per  cent,  alcohol  for  a  few  days  ; 
stain  in  picro-carmine  solution  for  some  hours  or  days  ;  and  tease  in  dilute 
glycerine. 

4.  Tear  off  a  small  shred  of  the  muscular  coat  of  a  piece  of  cat's  intestine 
which  has  been  for  48  hours  or  more  in  J  per  cent,  bichromate  of  potash 
solution  or  in  33  per  cent,  alcohol.  Hold  the  shred  with  forceps  in  a  drop  of 
water  and  fray  it  out  with  a  needle.  In  this  process  many  cells  will  be  set 
free  and  can  be  found  with  a  low  power.  The  preparation  may  then  be 
covered  and  examined  with  a  high  power.  Sketch  one  of  the  cells.  Then 
allow  dilute  hfematoxylin  solution  to  pass  under  the  cover-glass  and  lastly  a 
drop  of  glycerine.  Sketch  another  cell  after  staining.  Measure  two  or 
three  cells  and  their  nuclei. 


Ending  of  muscle  in  tendon. — A  small  tendon-bundle  passes  to 
each  muscular  fibre  and  becomes  firmly  united  with  the  sarcolemma, 
which  extends  over  the  end  of  the  fibre  (fig.  136).  Besides  this 
immediate    attachment,    a   further   connexion   is   established    by   the 

'This  method  is  the  one  given  by  Kanvier  (Traite  Technique,  p.  395).  The 
nuiscle-endings  may  also  sometimes  be  well  seen  at  the  extremities  of  the 
tendons  which  are  removed  from  the  mouse's  tail  in  the  manner  described  in 
Lesson  X. 


BLOOD-VESSELS   OF   MUSCLE. 


121 


fact   that  the  areohir  tissue  between  the  tendon  biuuUes  is  continuous 
witli  that  which  lies  between  the  muscular  fibres. 

Blood-vessels  of  muscle. — The  capillaries  of  muscular  tissue  are 
very  numerous.  They  run,  for  the  most  part,  longitudinally,  with 
transverse  branches,  so  as  to  form  long  oblong  meshes  (fig.  137). 
Ho  blood-vessels  ever  penetrate  the  sarcolemma.  In  the  red  muscles 
of  the  rabbit,   the  transverse  capillaries  have  small  dilatations   upon 


Fig.   136. — Termination   of  a  mus- 
cular    FIBRE     IN     TENDON.      (Ran- 

^'^^^•)  Fig.  137.— Capillary  vessels  of 

7)j,  sarcolemma ;    s,  the  same   membrane  MUSCLE, 

passing  over  the  end  of   the  fibre  ;   p,  , 
extremity    of    muscular    substance,    c, 
retracted   from   the    lower    end   of   the 
sarcolemma-tube ;     t,    a    tendon-bundle 
passing  to  be  fixed  to  the  sarcolemma. 

them  (fig.  13S).  Associated  with  this  and  other  peculiarities  of 
structure  (see  p.  115),  it  is  found  that  the  red  muscles  have  a  much 
slower  rate  of  contraction,  and  a  much  longer  period  of  latency  than 
the  ordinary  muscles. 

Lymph-vessels,  although  present  in  the  connective-tissue  sheath 
(perimysium)  of  a  muscle,  do  not  penetrate  between  the  component 
fibres. 

The   motor   nerves   of  voluntary   muscles   pierce    the    sarcolemma 


122 


THE   ESSENTIALS   OF   HISTOLOGY. 


and  terminate  in  ramified  expansions  knovvn  as  end-plates  or  motor 
end-organs  ;  the  sensoiy  nerves  end  in  groups  of  specially  modified  muscle 
fibres  known  as  mnsde-spiiulles  (see  Lesson  XIX.). 

Development.— Voluntary  muscular  fibres  are  developed  from  em- 
bryonic cells  of  the  mesoderm  (muscle-plate),  which  become  elongated, 
and  the  nuclei  of  which  become  multiplied,  so  as  to  produce  long 
slender  multi-nucleated  fusiform  or  cylindrical  embryonic  fibres. 
According  to  most  recent  authorities  the  embryonic  fibres  are  not 
formed  by  the  growth  of  a  single  cell,  but  by  the  joining  together 


Fig.  138. — Vascular  network  of  a  red  muscle  (semi-texdixosus)  ok  the 
RABBIT.     (Ranv'ier. ) 

o,  arteriole  ;  v,  v,  venules  ;  n,  dilatation  on  transverse  branch  of  capillaries. 


end  to  end  of  a  number  of  cells  of  the  muscle-plate  (or  even  of  more 
than  one  muscle-plate),  so  as  to  prbduce  a  syncytium,  within  which 
the  striated  fibrils  make  their  appearance.  These  appear  at  first 
along  one  side  of  the  fibre,  the  change  gradually  extending  around 
the  circumference  and  also  penetrating  towards  the  centre ;  but 
the  protoplasm  at  the  middle  of  the  fibre,  to  which  the  nuclei  are 
presently  confined,  and  at  the  side  opposite  to  that  at  which  the 
diSerentiation  began,  remains  for  some  time  unaltered  in  character 
(fig.  139).  Eventually  the  change  in  structure  extends  to  these  parts 
also,  and  the  nuclei  pass  gradually  to  occupy  their  ordinary  position 
under  the  sarcolemma,  which  has  by  this  time  become  formed.  The 
sarcolemma  is  "believed  to  be  produced,  not  by  the  muscle-fibre  itself. 


BLOOD-VESSELS   OF   MUSCLE. 


V23 


but  b}'  the  mcsench3'iue  or  connective-tissue  cells  between  the  fibres, 
since  it  is  directly  continuous  with  the  connective-tissue  bundles 
of  the  tendon  and  of  the  interstitial  tissue. 


Fig.  139. — Developing  muscular  fibres. 

A,  elongated  cell  with  two  nuclei.     A  striation  is  beginning  in  the  protoplasm  along  one 

.side  of  the  cell ;  from  fcetal  sheep.     (Wilson  Fox.) 

B,  from  human  ffetus  of  two  months.     (Ranvier.)     p,  central  protoplasm  with  several 

nuclei,  ii,  scattered  in  it ;   s,  commencing  sarcolemma,  with  striated  muscular  sub- 
.staiice  developing  immediately  beneath  it. 

C,  from  human  foetus  uf  three  months.     (Ranvier.)    The  contractUe  substance,  s,  f,  now 

almost  incloses  the  unaltered  protoplasm,  g  ;  only  one  nucleus,  n,  is  represented. 


CARDIAC   MUSCLE. 

The  muscular  substance  of  the  heart  is  composed  of  transversely 
striated  muscular  fibres,  which  differ  from  those  of  voluntary  muscle 
in  the  following  particulars,  viz.  :— their  striations  are  less  distinct ; 
they  have  no  sarcolemma,  although  there  is  a  thin  superficial 
layer  of  non-fibrillated  substance ;  they  branch  and  unite  by  their 
branches  and   also    at    the    side   with    neighbouring   fibres,   and  their 


124 


THE   ESSENTIALS   OF  HISTOLOGY. 


nuclei  lie  in  the  substance  and  often  near  the  centre  of  the  fibres. 
In  man  and  many  mammals  the  fibres  are  marked  off"  into  a  series  of 
short  cylindrical  cells  (figs.  140,  141)  joined  together  end  to  end  and 
side  to  side,  each  corresponding  to  one  of  the  nuclei.  The  junctions  of 
these  cells  may  be  seen  in  longitudinal  sections  appropriately  stained  ; 
they  come  also  distinctly  into  view  in  sections  of  the  fresh  tissue 
stained  with  nitrate  of  silver.  They  appear  to  be  bridged  across  by  fine 
fibrils,  continued  into  the  cells  above  and  below  the  lines  of  junction 
(fig.  143).  These  lines  have  usually  been  regarded  as  intercellular 
spaces  separating  the  constituent  cells  of  the  tissue  from  one  another 


f 


ii 


Fig.  140.— Muscular  fibres  from  the 
heart,  magnified,  showing  their 
cross-stri.e,  divisions,  and  junc- 
TIONS.    (Schweigger-Seidel.) 

The  nuclei  and  cell-junctions  are  only  repre- 
sented on  the  right-hand  side  of  the  figure. 


Fig.  141. — Six  muscular  fibre-cells 
FROM  THE  HEART.  (Magnified  425 
diameters. ) 

a,  line  of  junction  between  two  colls;  6,  c, 
branching  of  cells.  (From  a  drawing  by 
J.  E.  Neale.) 


(Schweigger-Seidel).  But  recent  authorities  (Przewosky,  v.  Ebner, 
M.  Heidenhain)  are  inclined  to  regard  the  cardiac  muscular  tissue 
as  forming  a  syncytium,  the  cells  being  all  continuous  both  laterally 
and  longitudinally,  and  the  apparent  intercellular  lines  being  special 
diff"erentiations.  These,  according  to  v.  Ebner,  are  due  to  localised  con- 
tractions, but,  according  to  Heidenhain,  represent  portions  of  the  fibres 
at  which  growth  in  length  occurs  (analogous  to  the  suture-lines 
between  the  flat  bones  of  the  cranium).  As  against  this  view  of  the 
structure  of  the  heart-muscle,  and  in  favour  of  that  of  Schweigger- 
Seidel,  must  be  set  the  silver-staining  of  the  supposed  cell-junctions, 
and  the  fact  that  it  is  easily  possible  in  some  animals  to  separate  the 
fibres  after  maceration  into  short  uninucleated  fragments  as  in  fig.  141. 


CARDIAC  MUSCLE. 


125 


The  short  non-nucleated  lengths  of  fibres  (fig.  142),  which  Heidenhain 
regards  as  fatal  to  the  cellular  theory,  may  be  parts  of  cells  lying 
in  other  planes  of  the  myocardium,  which  are  inserted  between  those 
belonging  to  the  plane  included  in  the  longitudinal  section.  On 
the  other  hand,  the  continuity  of  the  muscular  fibrils  within  the 
masses  of  Purkinje's  fibres  under  the  endocardium  in  the  sheep,  the 
fibrils  around  one  cell  being  freely  continued  around  the  neighbouring 
cells  (see  fig.  304,  p.  252),  is  in  favour  of  the  syncytial  theory.     Further, 


Fig.  142.  —  Diagram  of  segmextatiox 
OF  HEART  JIUSCLE.  (M.  Heidenhain.) 
Parts  op  the  segments  coxtaix  one 

OR   TWO    nuclei,    but    SOME   ABE    QUITE 
SMALL  AND  XON-NUCLEATED. 


,    iM 


fmrnm 


$\m^- 


Fig.  143. — Portiox  of  cardiac  muscle 

EXHIBITING       continuity      OF       FIBBILS 
ACROSS  JUNXTIONAL  LINE.     (Przewoskj.) 

Highlv  ma^uified 


in  many  vertebrates,  including  some  mammals,  no  cell-territories  can 
be  made  out  in  the  myocardium,  whilst  in  others,  and  especially  in 
man  and  some  mammals,  although  definite  cell-territories  can  be  shown 
to  exi.st  in  the  adult  condition,  they  are  absent  in  young  animals. 
We  must  therefore  conclude  that  both  conditions  may  occur. 

The  explanation  of  these  diff'erences  appears  to  lie  in  the  fact  that 
in  all  heart-muscle  at  a  certain  period  of  development  the  cells  form  a 
syncytium  within  which  the  contractile  fibrils  are  developed,  and  only  in 
mammals  is  a  differentiation  of  the  syncytium  into  cells  produced ;  the 
lines  of  junction  being  even  here  bridged  across  by  the  muscle-fibrils. 


126 


THE   ESSENTIALS   OF   HISTOLOGY. 


Non-striated,  Smooth  or  Plain  Muscle. 

Involuntary  or  plain  muscular  tissue  is  composed  of  long,  somewhat 
flattened,  fusiform  cells  (fig.  Hi),  which  vary  much  in  length.  Each 
cell  has  an  oval  or  rod-shaped  nucleus,  which  shows  the  usual  intra- 
nuclear network  and  commonly  one  or  two  nucleoli.    The  cell-substance 


A, 


Fig.  144.— Muscular  fibre-cells  from  the  muscular  coat  of 
the  small  intestine,  highly  magnified. 

A,  a  complete  cell,  showing  the  nucleus  with  intra-nuclear  network,  and 
the  longitudinal  fibrillation  of  the  cell-substance,  with  finely  vacuolated 
protoplasm  between  the  fibrils  ;  B,  a  cell  broken  in  the  process  of 
isolation  ;  a  delicate  external  layer  projects  at  the  broken  end  a  little 
beyond  the  striated  substance  of  the  cell. 


Fig.  144. 


Fig.  145.— Muscle-cells  of  intes-       Fig.  146.— Plain  muscle 


TINE.  (Szymonowicz.)  Magnified 
530  diameters. 
The  fibres  are  represented  in  longitudinal 
section  ;  and  the  interstices  between 
them  are  seen  to  be  bridged  across  by 
fine  fibrils,     i,  interstice  ;  n,  nucleus. 


FIBRE,       SHOWING       NU- 
CLEUS, centriole,  .\Nn 

CYTOPLASM     WITH     FIB- 
RILS.    (Lenhossek.) 


is  finely  fibrillated,  but  does  not  exhibit  cross-strise  like  those  of 
voluntary  muscle.  There  appears,  as  in  cardiac  muscle,  to  be  a 
delicate  non-striated  external  layer,  probably  a  stratum  of  undifferen- 
tiated protoplasm,  certainly  not  a  true  sarcolemma.  Next  to  this,  in 
some  smooth  muscle,  is  a  layer  containing  coarser  fibrils  (boundary 
fibrils  of  M.    Heidenhain).      There  is  a  little  intercellular  substance 


PLAIN    MUSCLE.  127 

which  can  be  stained  by  nitrate  of  silver,  and  which  is  Imdged  across 
liy  Hlaments  passing  from  cell  to  cell  (fig.  145).  Some  authorities, 
however,  deny  that  the  involuntary  cells  are  thus  connected,  and  hold 
that  the  appearance  of  bridging  fibres  is  due  to  intercellular  connective 
tissue.  It  is  however  difficult  to  understand  how  the  contractions  are 
propagated  from  cell  to  cell  if  there  is  no  sort  of  continuity  between 
the  cells. 

Plain  muscular  tissue  is  found  chiefly  in  the  walls  of  hollow  viscera  ; 
thus  it  forms  the  muscular  coat  of  the  stomach  and  intestine.s,  and 
occurs  abundantly  in  the  muscular  coat  of  the  gullet,  although  it  is 
here  intermixed  with  cross-striated  muscle ;  it  is  found  also  in  the 
mucous  membrane  of  the  whole  alimentary  canal  from  the  oesophagus 
downwards  ;  in  the  trachea  and  its  ramifications  ;  in  the  urinarv  l)ladder 
and  ureters;  in  the  uterus  and  Fallopian  tubes;  in  the  prostate;  the 
spleen  and  lymphatic  glands  ;  the  muscle  of  Miiller  in  the  orbit,  and 
in  the  ciliary  muscle  and  iris.  The  walls  of  gland-ducts  also  contain 
it :  and  the  middle  coat  of  the  arteries,  veins  and  lymphatics  is  largely 
composed  of  this  tissue.  It  occurs  in  the  skin,  both  in  the  secreting 
part  of  the  sweat  glands,  and  in  small  bundles  attached  to  the  hair- 
follicles  ;  in  the  scrotum  it  is  found  abundantly  in  the  subcutaneous 
tissue  (dartos),  and  it  also  occurs  in  the  areola  of  the  nipple. 

Development. — According  to  the  observations  of  C.  M'Gill,  the 
smooth  muscle  of  the  alimentary  canal  (pig)  is  developed  from  the 
syncytium  of  mesenchyme  cells  which  surrounds  the  entoderm. 
Some  of  these  cells  become  elongated  and  spindle-shaped  while 
retaining  their  inter-connexion.  Myofibrils  are  developed  in  their 
protoplasm.  These  are  not  confined  to  the  limits  of  a  single  cell,  but 
extend  over  two  or  even  a  large  number  of  cells.  The  myofibrils  are 
of  two  kinds,  coarse  and  fine,  varying  in  relative  number  in  different 
parts.  The  distinction  is  seen  even  in  the  fully  formed  muscle,  which 
retains  its  syncytial  character,  and  is  not  formed  of  completely 
separated  cells. 

In  certain  situations  smooth  muscle  is  formed  from  epithelium,  as 
with  the  muscular  tissue  of  the  sweat  glands  (Ranvier)  and  that  of 
the  iris  (Xussbaum,  Szili). 


128  THE  ESSENTIALS   OF  HISTOLOGY. 


LESSON    XVI. 

STRUCTURE  OF  NERVE-FIBRES. 

1.  Tease  a  piece  of  fresh  nerve  rapidly  in  salt  solution  (or  by  the  method  of 
seniidesiccation,  afterwards  mounting  in  salt  solution),  injuring  the  fibres  as 
little  and  obtaining  them  as  long  and  straight  as  possible.  Study  the  medul- 
lated  fibres,  carefully  noticing  all  the  structures  that  are  visible — viz.,  nodes 
of  Ranvier,  nucleus  of  primitive  sheath,  double  contour  of  medullary  sheath, 
medullary  segments,  etc.  Measure  the  diameter  of  half  a  dozen  fibres.  Draw 
a  short  length  of  a  fibre  very  exactly. 

2.  Prepare  a  piece  of  sympathetic  nerve  in  the  same  way.  The  nerves 
passing  to  the  spleen  are  well  adapted  for  the  study  of  non-medullated 
fibres.  They  may  also  be  found  amongst  the  medullated  fibres  of  the 
ordinary  nerves.     The  nuclei  may  be  stained  by  gentian  violet. 

3.  Separate  (in  dilute  glycerine)  into  its  fibres  a  small  piece  of  nerve  or 
nerve-root  that  has  been  twenty-four  hours  in  1  per  cent,  osmic  acid.  The 
nerve  should  have  been  moderately  stretched  on  a  piece  of  cork  by  means  of 
glass  pins  before  being  placed  in  the  acid.  Keep  the  fibres  as  straight  as 
possible  and  only  touch  them  near  their  ends  with  the  needles.  Sketch  two 
portions  of  a  fibre  under  a  high  power,  one  showing  a  node  of  Ranvier  and 
the  other  a  nucleus  of  the  primitive  sheath.  Look  for  fibres  of  Remak. 
Measure  the  length  of  the  nerve-segments  between  the  nodes  of  Ranvier. 

4.  Mount  in  xylol  balsam  or  dammar  sections  of  a  nerve  which  has  been 
hardened  in  picric  acid  and  alcohol,  or  fixed  with  osmic  acid  and  hardened 
in  alcohol.  The  sections  may  be  stained  with  picro-carmine  or  hsematoxylin. 
The  nerve  should  be  pinned  out  straight  upon  a  cork  with  glass  pins  before 
being  placed  in  the  hardening  solutions.  Examine  the  sections  first  with 
a  low  and  afterwards  with  a  high  power.  Notice  the  lamellar  structure  of 
the  j^erineurium,  the  varying  size  of  the  nerve-fibres,  the  axis  cylinder  in 
the  centre  of  each  fibre,  etc.  Measure  the  diameter  of  five  or  six  fibres, 
and  sketch  a  small  portion  of  one  of  the  sections. 

5.  Study  sections  of  splenic  nerve  placeil  as  soon  as  possible  after  death 
in  Flemming's  solution. 

6.  Teased  })reparations  and  sections  from  nerves  which,  some  days  pre- 
viously, have  been  cut  nearer  the  spinal  cord.  The  nerves  should  have  been 
prepared  with  osmic  acid,  as  in  ^  3.  Notice  the  breaking  up  of  the  myelin 
of  the  medullary  sheath,  varying  in  degree  according  to  the  length  of  time 
the  section  has  been  made  previously.  In  pre])arations  from  the  central 
cut  end  of  the  nerve  prepared  by  Cajal's  reduced  silver  method  ^  new  fibres 
may  be  seen  budding  from  near  the  extremities  of  the  undegenerated  fibres 
of  the  stump. 


Nerve-fibres  are  of  two  kinds,  medullated  and  non-medtdlated.     The 
cerebro-spinal  nerves  and  the  white  matter  of  the  nerve-centres  are 

^  See  Appendix. 


STRUCrrUKE   OF   NEUVK-FIBRKS. 


129 


composed    of  medullated   fibres;   the  sympathetic    nerves  near  their 
peripheral  distiibution  are  largely  made  up  of  non-medullated  fibres. 


Fig.  147. —"White  or  medullated 
nerve-fibbes,  showing  the  sinuous 
outline  and  double  contours. 


Fig.  148.— Portions  of  two  nerve- 
fibres  STAINED  with  OSMIC  ACID, 
FROM  A  YOUNG  ANIMAL.  (Diagram- 
matic.) 

i?,  R,  constrictions  of  Ranvier,  with  axis- 
cylinder  passing  through,  a,  neurolemma 
of  the  nerve  ;  c,  opposite  the  middle  of  the 
segment,  indicates  the  nucleus  and  proto 
plasm  Ij-ing  between  the  primitive  sheath 
and  the  medullary  sheath.  In  A  the  nodes 
are  wider,  and  the  intersegmental  sub- 
stance more  apparent  than  in  B. 


mm 


Fig.  148. 


The  medullated  or  white  fibres  are  characterised,  as  their  name 
implies,  by  the  presence  of  the  so-called  medullar!/  sheath  or  white 
substance.     This   is   a   layer  of  soft   substance,    physically  of  a   fatty 


130 


THE   ESSENTIALS   OF   HISTOLOGY". 


nature,  which  encircles  the  essential  part  of  a  nerve-fibre,  viz.,  the 
axis-cylinder.  Outside  the  medullary  sheath  is  a  delicate  but  tough 
homogeneous  membrane,  the  primitive  sheath  or  nucleated  sheath  of 
Schicann,  but  this  is  not  present  in  all  medullated  fibres,  being  absent 
in  those  which  are  within  the  nerve-centres.  The  primitive  sheath  is 
known  as  the  neurolemma?- 


ifeStri 


ii'i 


Fig.  149.— a  small  part  of  a  ^iedullated 
FIBRE.     (Highly  magnified. ) 

The  fibre  looks  in  optical  section  like  a  tube— 
heuce  the  term  tubular,  formerly  applied  to 
these  fibres.  Two  partial  breaches  of  continuity 
(medullary  clefts)  are  seen  in  the  medullary 
sheath,  which  at  these  places  exhibits  a  tendency 
to  split  into  laminfe.  The  primitive  sheath  is 
here  and  there  apjiarent  outside  the  medullary 
sheath,  and  the  delicate  stria?  which  are  visible 
in  the  middle  of  the  fibre  indicate  the  fibrilla- 
tions of  the  axis  cvlinder. 


w. 


Fig.  I.'jO. — Two  portions  of  medul- 
lated NERVE  FIBRES,  AFTER  TREAT- 
MENT WITH  O.SillC  ACID,  SHOWING  THE 
AXIS-CYLINDER  ANI;  THE  MEDULLARY 
AND    PRIMITIVE    SHEATHS.      (Kej    and 

Retzius. ) 
A,  node  of  Ranvier.  B,  middle  of  an  inter- 
node  with  nucleus,  c,  axis-cj'linder  pro- 
jecting ;  p,  primitive  sheath,  within  which 
the  medullary  sheath,  which  is  stained 
dark  by  the  osmic  acid,  is  broken  away 
for  a  short  distance. 


The  medullary  sheath  is  composed  of  a  highly  refracting  fatty  material 
(myelin),  which  gives  a  characteristic  dark  contour  and  tubular  appearance 
to  the  nerve-fibres  (fig.  147).  It  afiords  a  continuous  investment  to  the 
axis-cylinder,  except  that,  as  was  shown  by  Ranvier,  in  the  peripheral 
nerve-fibres  it  is  interrupted  at  regular  intervals.  At  these  places  the 
neurolemma  appears  to  produce  a  constriction  in  the  nerve-fibre,  and 
the  interruptions  of  the  medullary  sheath  are  accordingly  known  as 
the  constrictions  (Ranvier)  or  nodes  (figs.  148,  151),  the  latter  term 
being  applied  from  the  resemblance  which  they  bear  to  the  nodes 
of  a  bamboo.     It  is,   however,   uncertain  whether  the  constriction  is 

1  Often  termed  "neurilemma,"  a  name  formerly  applied  also  to  the  sheath 
of  Henle  (see  p.   136). 


NERVE- FIBRES.  i:il 

entirely  occupied  by  the  neurolemma  itself  or  partly  by  a  special 
band  (constricting  band  of  Ranvier)  of  a  material  which  resembles 
intercellular  substance  in  its  reaction  to  nitrate  of  silver  (fig.  16"J). 
The  length  of  nerve  l)etween  two  successive  nodes  is  termed  an  inter- 
node  ;  in  the  middle  of  each  internode  is  one  of  the  nuclei   of  the 


Fig.  151. — Nerve-fibre  prepared  with  osmic  acid.     (Szymonowicz.) 

6,  constriction  of  Rauvicr.     The  intervals  between  the  modulliuy  sognicnt.s  appear  as 
clear  oblique  lines,  «,  a. 

neurolemma.  Besides  these  interruptions  the  medullary  sheath  shows 
a  variable  number  of  oblique  clefts  (Lantermann)  (figs.  149,  151),  sub- 
dividing it  into  irregular  portions,  which  have  been  termed  medullary 
segments ;  but  there  is  some  reason  to  believe  that  the  clefts  are 
artificially  produced.  At  the  clefts  there  is  an  appearance  of  spiral 
fibres  in  the  medullary  sheath,  especially  after  treatment  of  the  nerve 


Fig.  152. — Spiral  and  reticular  fibrils  ix  the  sheath  of  a  nerve- 
fibre,     (fiolgi.) 

with  certain  reagents  (Golgi)  (fig.  152);  it  is,  however,  possible  that 
this  appearance  does  not  represent  any  pre-existing  structure. 
A  reticular  appearance  has  also  been  described  in  the  medullary  sheath 
(neurokei'aiin  network  of  Kiihne),  and  can  be  readily  seen  in  nerve  fibres 
fixed  in  alcohol  and  treated  with  ether,  but  it  varies  greatly  in 
aspect,    and    is    perhaps    produced    by    the   action   of  the    reagents 


Fig.  153.^Recticular  aitearance  in  the  medull.vry  she.\th  of  a 
nerve-fibre.     (Gedoelst.)     (From  the  guinea-pig. ) 


employed  to  show  it  (figs.  152,  153).  By  other  modes  of  fixation 
{e.g.  picric  acid)  the  medullary  sheath  seems  to  have  a  rod-like 
structure  (fig.  155) ;  this  again  may  be  due  to  the  manner  in  which 
certain  of  its  constituents  are  coagulated  by  the  reagent.  Osmic  acid 
stains  the  medullary  sheath  black  (figs.  151,  154,   156). 


132 


THE   ESSENTIALS   OF   HISTOLOGY. 


The  axis-ci/linder,  which  runs  along  the  middle  of  the  nerve-fibre,  is 
a  soft  transparent  thread  which  is  continuous  from  end  to  end  of  the 
nerve.  On  account  of  the  peculiar  refractive  nature  of  the  medullary 
sheath  it  is  difficult  to  see  the  axis-cylinder  in  the  fresh  nerve  except  at 
the  nodes,  where  it  may  be  observed  stretching  across  the  interruptions 


Fig.  154. — Longitudinal  .\xd  transverse  section  of  medullatkd  nerve- 
fibre  OF  FROG  (osMic  ACID  AND  ACID  fuchsine).     (After  Biedermaiin. ) 

The  longitudinal  section  shows  one  node  of  Ranvier  and  two  of  Lanterniann's  clefts. 
The  fibi-illar  structure  of  the  axis-cylinder  is  shown  in  both  longitudinal  and 
transverse  section. 


/^^>X 


in  the  medullary  sheath  ;  it  may  also  sometimes  be  seen  projecting 
from  a  broken  end  of  a  nerve-fibre.  It  is  longitudinally  striated,  being 
made  up  of  exceedingly  fine  fibrils  {nenro-fihrils,  fig.   154).     They  are 

readily  seen  at  the  terminations 
of  nerves  as  in  the  cornea  and  are 
also  visible  in  the  section  of  a  nerve- 
fibre  as  fine  dots  (fig.  lo-t),  which 
sometimes  appear  to  have  a  clear 
centre  (fig.  155),  as  if  the  fibrils 
were  tubular.  Staining  with  nitrate 
of  silver  produces  a  curious  trans- 
versel}"  striated  appearance  in  the 
axis-cylinder  (Fromann)  (fig.  162,  c), 
but  this  is  due  to  the  precipita- 
tion of  chlorides,  and  does  not 
indicate  a  pre-existing  structure 
(Macallum). 

Medullated      nerve  -  fibres      vary 
greatly  in  size  (figs.  155,  156),  but 
may    be   classified    as    large,    inter- 
mediate, and  small.     The  largest  are 
those  which  are  passing  to  the  skin  and  to  the  voluntary  muscles  :  the 
smallest  are  those  which  are  distributed    to   the  viscera   and    blood- 
vessels by  way  of  the  autonomic  nerves.  ^     As  shown  by  Gaskell,  the 

'This  term  has  been  introduced  by  Laugley  to  include  both  the  nerves  of 
the  sympathetic  system  and  also  the  analogous  nerves  which  proceed  from  the 
cranial  and  sacral  regions  for  the  innervation  of  certain  involuntary  muscles 
and  secreting  glands. 


Fig.  ICio. 

FIBRES. 


-Section  across  five  nerve- 
(Magnified  1000  diameters. ) 


The  nerve  was  hardened  in  picric  acid  and 
stained  with  picro-carmine.  The  radial 
striation  of  the  medullary  sheath  is  very 
apparent.  In  one  fibre  the  i-aysare  broken 
by  shrinkage  of  the  axis-cylinder.  The 
fibrils  of  the  axis-cylinder  appear  tubular. 
(From  a  photogi-aph.) 


NERVE-FIBRES. 


133 


anterior  roots  of  the  last  one  or  two  cervical  nerves,  of  all  the 
thoracic,  of  the  first  and  second  lumbar,  and  of  the  second  and  third 
sacral  nerves  contain  besides  the  ordinary  large  medullated  fibres  a 
bundle  of  very  small   medullated  fibres  which  are  destined  for  the 


Fig.  1.56. — Section  of  the  sciatic  nerve  of  a  c.\t,  showing  the  vakiations 
IN  SIZE  OF  ITS  constituent  FIBRES.  (Magnified  ;W0  diameters.)  The 
nerve  was  fixed  with  osinic  acid. 


viscera  and  blood-vessels,  and  which  for  the  most  part  pass  to  the 
sympathetic  system.  The  roots  of  some  of  the  cranial  nerves  (the 
spinal  accessory,  vagus,  glossopharyngeal,  and  facial)  contain  similar 
fine  medullated  fibres. 

Non-medullated  fibres. — Intermingled   with   the   medullated    fibres 
there  may  always,  even  in  the  cerebro-spinal  nerves,  be  found  a  certain 


Fig.  157. — Non-medullated  nekve-fibres.     (Magnified  400  diameters.) 


number  of  pale  fibres  devoid  of  the  dark  double  contour  which  is 
characteristic  of  the  presence  of  a  medullary  sheath.  These  are  the 
grey  OT  non-medullated  fibres,  also  called,  after  their  discoverer,  ^5re5  of 
Remak   (fig.    157).     They   frequently   branch,    Avhich    the   medullated 


134 


THE   ESSENTIALS   OF   HISTOLOGY. 


fibres  rarely  do  except  near  their  termination,  and  they  are  beset 
with  numerous  nuclei  which  perhaps  belong  to  a  delicate  sheath, 
but  this  is  not  certain,  and  undoubtedly  both  in  longitudinal  view  and 
in  cross  section  the  nuclei  seem  to  lie  in 
the  substance  of  the  fibres.  The  sympathetic 
nerves,  as  they  approach  their  peripheral  dis- 
tribution, are  largely  made  up  of  fibres  of  this 
nature,  but  man}?^  of  the  fibres  contained  in 
the  sympathetic  nerves  possess  a  thin  medul- 
lary sheath,  and  have  the  usual  structure  of 
medullated  fibres. 

Structure  of  the  nerve-trunks. — In  their 
course  through  the  body  the  nerve-fibres  are 
gathered  up  into  bundles  or  funiculi,  and  the 
funiculi  are  again  united  together  to  form  the  nerves  which  we 
meet  with  in  dissection.  The  connective  tissue  which  unites  the 
funiculi  and  invests  the  whole  nerve,  connecting  it  to  neighbouring 


Fig.  158. — Section  across 
non-medullated  fibres 
from  the  splenic  nerve 
OF  THE  OX.     (Tuckett.) 


Fig.  1.59. — Section  op  part  of  a  nerve-trunk  fixed  with  osmic  acid. 
(From  a  photograph.)     Magnified  40  diameters. 

Three  small  funiculi  and  a  small  part  of  a  larger  funiculus  are  shown.     The  fat-cells  in 
the  epineurium  are  stained  black  by  the  osmic  acid. 


parts  and  conveying  to  it  blood-vessels,  lymphatics,  and  even  nerve- 
fibres  destined  for  its  coats,  is  termed  the  cfineurium  ;  it  frequently 
contains  fat-cells.  That  which  ensheaths  the  funiculi  is  known  as 
the  perineurium  (figs.  L59  to  161).  It  has  a  distinctly  lamellar 
structure  (fig.  160),  the  lamellae  being  composed  of  connective 
tissue  covered  by  flattened   epithelioid  cells  (fig.    162,  a).     Between 


STRUCTURE   OF   NERVE-TRUNKS. 


135 


the  lamellae  are  clefts  for  the  conveyance  of  lymph  to  the  lymphatics 
of  the  epineurium.  The  delicate  connective  tissue  which  lies  between 
the    nerve-fibres  of  the   funiculus  is  the  endoneurinni.      It   assists   in 


r    '       <r 

^^    1 


Fig.  160. — Section  of  part  of  a  funiculus  of  the  sciatic  nerve  of  a  cat 
FIXED  WITH  Flemming's  SOLUTION.     Magnified  400  (liametera. 

cp,  epineuriuru  with  blood-vessels  ;  e,  section  of  an  end-bulb  ;  p,  perineurium  ;  m,  medul- 
lated  fibre  cut  at  the  level  of  a  nucleus  :  n,  n,  bundles  of  non-medullated  fibres. 


^^-r: 


^.tf^?^ 


h 


^ 


Fig.  161. — Section  of  the  thoracic  sympathetic  coed  of  the  cat. 
(Fischer.)     Osmic  preparation. 

The  nerve  is  composed  in  almost  equal  parts  of  fine  medullated  fibres  (3,  4)  derived  from 
the  thoracic  anterior  roots,  and  grey  fibres  (.5)  derived  from  the  syrupathctic 
ganglion-cells.     The  dark  bodies  in  the  epineurium  (l)are  fat-cells  ;  2,  perineurium. 

supporting  the  longitudinally  arranged  meshwork  of  blood-capillaries, 
and  its  interstices  communicate  with  the  lymph-clefts  of  the 
perineurium. 

All  the  branches   of  a  nerve,  and  even  sinojle    nerve-fibres  which 


136 


THE   ESSENTIALS   OF   HISTOLOGY 


are  passing  to  their  distribution,  are  invested  with  a  prolongation  of 
the  perineural  sheath,  which  is  then  known  as  the  sheath  of  Henle. 


200 

I 


%ulm^'\ 


<m\m~\ 


200 

1 


4.     + 


'^ 


W^^   1  •■■nip 


Fig.  162. — Xerves  stalned  with  silvee  yixRAXE.     (Ranvier.) 

In  A,  the  epithelial-like  layer  of  flattened  cells  belonging  to  the  sheath  of  Henle  is 
stained.  In  B,  the  cross-like  markings  at  the  nodes  are  exhibited.  In  C,  a  single  fibre 
is  shown  more  highly  magnified,  with  Fromann's  transverse  markings  of  the  axis- 
cylinder,     a,  constricting  band  ;  to,  medullary  sheath  ;  cy,  axis-cylinder. 

The  nerve-trunks  themselves  receive  nerve-fibres  {nervi  nenwum) 
which  ramify  chiefly  in  the  epineurium  and  terminate  within  this 
in  end-bulbs  (Horsley)  (fig.  160,  e). 

The  degenerative  processes  which  occur  in  cut  nerve-fibres  as  well 
as  the  subsequent  reparative  processes  will  be  dealt  with  after  the 
structure  of  nerve-cells  has  been  studied  (see  p.   154). 


NERVE-CELLS.  137 


LESSONS   XVII.    AND   XYIII. 

NERVE-CELLH. 

1.  Put  a  small  piece  of  spinal  ganglion  into  1  per  cent,  osmic  acid  for  a 
few  hours.  Place  in  water  containing  a  fragment  of  thymol  for  two  days 
or  more.  Tease  in  dilute  glycerine.  Notice  the  spheroidal  ganglion-cells  ; 
their  large  nuclei  and  distinct  nucleoli.  Many  of  the  cells  may  still  be  seen 
within  their  nucleated  membranous  sheath.  Look  for  cells  which  still  retain 
the  axis-cylinder  process  and  for  T-shaped  junctions  of  nerve-fibres  with 
this.  Fat-cells  may  be  present  in  the  periganglionic  connective  tissue. 
These  will  appear  intensely  black  in  osmic  preparations. 

2.  Prepare  in  the  same  way  a  spinal  ganglion  or  the  Gasserian  ganglion 
of  the  skate  or  cod.     Notice  the  bipolar  character  of  most  of  the  cells. 

3.  Prepare  a  piece  of  sympathetic  ganglion  as  in  §§  1  and  2.  If  from  a 
rabbit  observe  that  many  of  the  cells  are  bi-nucleated. 

Measure  two  or  three  cells  in  each  of  the  above  preparations. 

4.  Mount  stained  sections  of  ganglia,  both  spinal  and  sympathetic.  These 
■will  serve  to  show  the  arrangement  of  the  cells  and  fibres  in  the  ganglion 
and  the  nucleated  sheaths  aroinid  the  nerve  cells. 

The  ganglia  may  be  fixed  and  hardened  in  saturated  solution  of  corrosive 
sublimate  or  of  picric  acid  or  in  10  per  cent,  formol.  They  may  either  be 
stained  in  bulk  or  sections  cut  from  paraffin  and  stained  on  the  slide  bv 
Nissl's  method.  Ehrlich's  methylene  blue  method,  Golgi's  silver  chromate 
method,  or  Cajal's  silver  reduction  method,  especially  the  last  named,  are 
all  useful  for  showing  the  cells  and  their  connections  with  nerve-fibres. 
These  methods  are  described  in  the  Appendix. 

5.  Place  a  portion  of  the  grey  matter  from  a  piece  of  spinal  cord  in  33  per 
cent,  alcohol.  After  macerating  for  two  days  or  longer  in  this  fluid,  a  little  of 
the  grey  matter  may  be  shaken  up  in  a  test-tube  with  water  so  as  to  bieak  it 
up  into  fine  fragments.  Allow  these  to  subside,  decant  off  the  water  and 
substitute  a  dilute  solution  (1  to  500)  of  methylene  blue  or  solution  of 
picrocarmine.  When  it  appears  sufficiently  stained  some  of  the  debris  is 
pipetted  off  and  examined  under  a  low  power  of  the  microscope  ;  at  first 
without  a  cover-glass  so  that  the  cells  may,  if  necessary,  be  separated  from 
the  rest  of  the  tissue.  Mount  in  water  with  a  thick  hair  under  the  cover- 
glass.  Notice  the  large  branching  cells,  some  with  a  mass  of  2:>igment  near 
the  nucleus.  Observe  the  fibrillation  of  the  cell-processes.  Many  axis- 
cylinders  will  be  seen  in  this  preparation  deprived  wholly  or  partially  of 
their  medullary  sheath,  and  their  fibrillar  structure  can  then  also  be  well 
seen.  C'arefiilly  sketch  these  appearances.  To  keep  the  methylene  blue 
preparation  the  stain  must  be  fixed  with  picrate  of  ammonia,  after  which 
a  mixture  of  glycerine  and  pici'ate  of  ammonia  may  be  used  for  mounting. 
If  picrocarmine  is  used  the  specimen  is  simply  preserved  in  dilute  glycerine. 
Similar  preparations  may  be  made  from  the  grey  matter  of  the  cerebral 
cortex  and  cerebellar  cortex. 


138  THE   ESSENTIALS   OF   HISTOLOGY. 

6.  Examine  sections  of  s])iiial  cord,  medulla  oblongata  and  brain  stained 
by  methylene  blue  (Nissl's  method),  to  exhibit  the  angular  particles  within 
the  nerve-cells. 

7.  Examine  sections  of  parts  of  brain,  spinal  cord  and  ganglia  jirepared  by 
Cajal's  method,  to  exhibit  the  neuro-fibi'ils  in  the  cells  and  cell-processes. 

8.  Examine  the  nerve-cells  and  neuroglia-cells  in  sections  from  the  spinal 
cord,  cerebrum,  or  cerebelluru  of  a  small  animal,  e.g.  young  rat  or  kitten, 
pre|)ared  by  Golgi's  method.  The  sections  must  be  mounted  in  thick  xylol 
balsam  or  dammar  varnish,  without  a  cover-glass,  and  dried  lapidly  on  a 
warm  plate. 

9.  Examine  sections  of  spinal  cord  (lumbar  enlargement)  and  correspond- 
ing spinal  ganglia  from  an  animal  in  which  the  sciatic  nerve  had  been  cut 
about  three  weeks  before  it  was  killed.  The  sections  are  to  be  stained  by 
Nissl's  method.  Many  of  the  anterior  horn  nerve-cells  and  of  the  ganglion- 
cells  on  the  side  of  the  lesion  will  exhibit  the  chromatolysis  or  breaking  down 
of  the  Nissl  granules,  which  is  characteristic  of  cells  the  axons  of  which  have 
been  severed.    They  may  be  compared  with  the  normal  cells  on  the  intact  side. 


Nerve-cells,  neurocytes  or  neurones. — Nerve-cells  occur  in  the  grey 
matter  of  the  nerve  centres,  and  in  little  groups  on  the  course  of 
certain  of  the  peripheral  nerves,  these  groups  often  causing  nodular 
enlargements  of  the  nerves,  which  are  knoAvn  as  (janglia.  The  most 
conspicuous  ganglia  are  those  which  are  found  vipon  the  posterior  roots 
of  the  spinal  nerves,  upon  the  roots  of  some  of  the  cranial  nerves, 
and  upon  the  trunk  and  principal  branches  of  the  sympathetic  nerve. 
Minute  ganglia  are  also  found  very  numerously  in  connection  with  the 
nerves  which  are  supplied  to  glands  and  involuntaiy  muscular  tissue, 
as  in  the  salivary  glands,  heart,  alimentary  canal,  bladder,  uterus,  etc. 

Nerve-cells  A^ary  much  in  size  and  shape ;  many  are  large, 
some  being  amongst  the  largest  cells  met  with  in  the  body,  but 
others  are  quite  small.  All  nerve-Cells  possess  at  least  one  process, 
the  axon,  which  becomes  either  a  non-medullated  fibre  or  the  axis- 
cylinder  of  a  medullated  fibre.  If  other  processes  are  present  they 
are  always  branched  almost  from  their  commencement  at  the  cell-body, 
and  they  are  therefore  termed  dendrons  (dendrites).  The  nucleus  is 
generally  large,  clear,  and  spherical,  with  a  single  large  and  distinct 
nucleolus ;  there  may  also  be  a  network  of  chromatin,  but  this  is 
not  always  to  be  seen.  The  cj^toplasm  is  tibrillated,  the  fibrils 
passing  into  the  processes;  they  are  known  as  neuro-fibrils  (p.  132), 
and  are  believed  to  be  the  actual  conductors  of  nerve-impulses.  It 
also  contains  peculiar  angular  particles  {Nisd  granidcs)  staining  deeply 
with  methylene  blue,  but  the  size,  number,  and  arrangement  of  these  in 
different  cells  vary  greatly  (fig.  163).  The  granules  also  vary  in  number 
and  size  with  the  physiological  condition  of  the  cells ;  thus  it  is  found 


i 


NERVE.CELLS 


139 


Fig.  163.— Multipolar  and  unipolar  types  of  nervk-cell. 

A,  Large  pyramidal  cell  of  cerebral  cortex,  human.    Nissl  method.    (Cajal.)   a,  axon ; 

h,  cell-bodj^ ;  c,  apical  dendi-oii  ;  d,  placed  between  two  of  the  basal  dendrons 
points  to  the  nucleus  of  a  neuroglia  cell. 

B,  Unipolar  cell  from  spinal  ganglion  of  rabbit.     Nissl  method.     (Cajal.)    a,  axon  ; 

b,  circumnuclear  zone,  poor  in  granules ;  c,  capsule ;  d,  network  within  nucleus ; 
e,  nucleolus. 


140 


THE   ESSENTIALS   OF   HISTOLOGY. 


that  nerve-cells  which  have  been  fatigued  by  prolonged  activity  (fig. 

164),  and  also  those  the  axis-cylinder  process  of  which  has  been  cut 

(fig.  165),  show  the  Nissl  granules 
becoming  disintegrated ;  they  may 
even  disappear  for  a  time  from 
the  cell.  A  similar  result  is  found 
to  occur  after  the  action  of  poisons 
which  especially  affect  the  nervous 
system.  The  Nissl  granules  of 
the  nerve-cell  appear  to  consist 
chemically  mainly  of  nucleoproteid ; 
they  contain  organically  combined 
iron  (Macallum).  Many  nerve-cells 
have  also  a  clump  of  pigment- 
granules,  containing  lecithin,  at 
one  side  of  the  nucleus.  This  is 
especially  marked  in  certain  locali- 
ties (locus  coeruleus,  locus  niger), 
and  is  more  frequent  in  man  than 
in  the  lower  animals.  The  pigment 
also  tends  to  increase  in  amount  as 


I 


Fig.  164. 


-Two   MOTOR  NERVE-CELLS 
FROM   THE   DOG. 
a,    normal ;     b,    after  a  period   of    prolonged 
activit}'.     (Photographed  from  preparations    age    advailCCS. 
by  Dr.  Gustav  Mann.)  ° 

As  already  stated,  the  body  of 
every  nerve-cell  is  traversed  by  fine  fibrils  (neuro-Jibrils)  continuous 
with  those  in  the  axis-cylinder  of  the  issuing  nerve  and  with  similar 


Fig.  165. — Chromatolysis  of  nerve-cells,  produced  by  severance  of  axon. 

(Diagrammatic.) 

A,  Nissl  granules  normal ;  B,  commencing  chromatolysis,  the  cell  and  nucleus  swollen 
and  the  granules  beginning  to  disintegrate  (the  nucleus  is  usually  close  to  the 
periphery  at  this  stage);  C,  advanced  condition  of  chromatolysis,  the  cell  and 
nucleus  shrunken. 


NERVE-CELLS.  141 

fibrils  in  their  dendrons.  They  were  noticed  by  Max  Schultze,  but 
their  course  and  connections  were  first  accurately  described  by  Apathy 
in  the  nerve-cells  of  certain  annelids.  They  can  be  seen  without  any 
difficulty  in  the  nerve-cells  of  vertebrates  (fig.   166)  by  the  employ- 


FiG.  166. — Neeve-cells  of  kitten  (froji  the  anterior  corpora  quadrigemina) 
SHOWING  neuro-fibrils.    (Cajal.) 

II,  axon  ;  6,  c,  d,  various  parts  of  the  intracellular  plexus  of  fibrils. 

ment  of  the  silver  reduction  method  of  Cajal.  The  neuro-fibrils 
are  said  to  present  variations  in  thickness  according  to  the  condition 
of  activity  of  the  animal  at  the  time  of  death. 

Most,  if  not  all,  nerve-cells  show  a  delicate  superficial  reticulum 
(fig.  167),  described  by  Golgi,  which  is  generally  regarded  as  composed 
of  neuro-fibrils,  but,  according  to  J.  Turner,  may  be  an  investment 
derived  from  neuroglia-cells.     Golgi  has  also  described  another  network 


142 


THE   ESSENTIALS  OF   HISTOLOGY. 


of  fibrils  with  somewhat  larger  meshes  {deep  reticulum  of  Golgi)  (fig.  168) 
in  the  deeper  parts  of  the  cell.     According  to  some  authorities  both 


&^ 


Fig.  167. — Superficial  network  of  golgi  .surrounding 
two  cells  from  the  cerebral  cortex  of  the  cat; 
ehrlich's  method.     (Cajal.) 
A,  large  cell ;  B,  small  cell,     a,  a,  folds  in  the  network ;  b,  a  ring- 
like condensation  of  the  network  at  the  poles  of  the  larger 
cell ;  c,  spinous  projections  from  the  surface. 


Fig.  168. — Nerve-cell  from  spinal  ganglion,  showing 

NETWORK   around  THE  NUCLEUS.      (Golgi.) 


ill 

Fig.   169.— Axis-cylinder 

PROCESS      of      a      nerve- 
cell    FROM     THE     SPINAL 

CORD.  (M.  Schultze.) 
X  X ,  portion  of  the  cell-body, 
out  of  which  the  fibrils  of 
the  axis-cylinder  process,  o, 
are  seen  to  emerge.  At  «', 
this  process  acquires  a 
medullary  .sheath.  (Highly 
magnified.) 


NERVE-CELLS. 


143 


superficial  cand  deep  networks  are  in  continuity  throughout  the  cell, 
and  receive  and  are  prolonged  from  the  neuro-fibrils  of  an  entering 
axon  on  the  one  hand,  and  with  those  of  the  axis-cylinder  process  of 
the  nerve-cell,  and  also  of  the  dendrons,  on  the  other  hand.  Other 
authorities  regard  these  networks  as  distinct  from  the  neuro-fibrils, 
which  they  suppose  to  run  independently  through  the  nerve-cell  body, 
entei-ing  it  by  way  of  the  dendrons  and  emerging  in  the  axon. 

Trophospongium  of  NERVE-CELi.s. — Entirely  distinct  from  the  fibrils 
is  a  system  of  fine  canaliculi,  which  has  been  described  by  E.  Holmgren, 
permeating  the  cytoplasm  of  the  nerve-cell  body  for  the  purpose 
of  subserving  its  nutrition  by  conveying  plasma  into  its  substance  (see 
fig.  4,  p.  4).  These  channels  are  stated  by  Holmgren  to  be  occupied  by 
branching  processes  of  other  (connective-tissue  or  neuroglia)  cells.  In 
the  very  large  nerve-cells  from  which  the  nerves  of  the  electric  organs 
of  Malapterurus  arise  blood-vessels  penetrate  into  the  cytoplasm. 


Fig.  170.— Two  bipolar  g.-^nglion  cells  (fish).     (Holmgren.) 
In  B  the  medullar}-  sheath  is  continued  as  a  thin  layer  over  the  oell-hody. 


Processes  of  nerve-cells. — As  already  intimated  the  processes  are  of 
two  kinds.  The  first  is  that  known  as  the  axis-cylinder  process  (Deiters) 
or  nerve-fibre  process,  so  called  because  it  becomes  the  axis-cylinder 
of  a  nerve-fibre  (fig.  169  a,  a);  in  the  case  of  the  non-medullated 
fibres,  it  becomes  the  nerve-fibre  itself.  It  is  also  termed  the  neuraxon 
or  simply  the  axon. 

Probably  no  nerve-cell  is  without  this  process.  The  place  where  it 
arises  from  the  body  of  the  nerve-cell  {cone  of  origin)  is  marked  off  from 
the  rest  of  the  cell-substance  by  absence  of  Nissl  granules  (see  fig.  163). 
The  other  processes  of  the  nerve-cell  are  those  which  were  termed 
by  Deiters  the  protoplasmic  processes ;  they  are  now  usually  termed  the 


144  THE   ESSENTIALS   OF   HISTOLOGY. 

dendrons  or  dendrites  and  are  generally  multiple,  whereas  the  axon 
is  generally  single.  The  dendrons  are  characterised  by  the  fact  that 
as  soon  as  they  leave  the  cell  they  begin  to  branch  dendritically, 
whereas   the    axis-cylinder   process    does   not   branch    until    near   its 


Fig.  171. — Vakiods  forms  of  pericellular  ending  of  entering  nerve  fibres 
IX  THE  TRAPEZOID  NUCLEUS  OF  THE  CAT.     (Edinger,  after  Veratti. ) 

termination,  with  the  exception  of  a  few  fine  lateral  offshoots,  which 
are  sometimes  given  off  in  its  course.  Dendrons  may  be  absent ; 
the  cell  is  then  adendric.  Most  nerve-cells  have  only  one  nerve-fibre 
process  (unipolar),  but  some  have  two  or  more  (bipolar,  multipolar). 
The  dendrons  contain  Nissl's  granules,  but  the  axons  do  not. 


PROCESSES  OF   NERVE-CELLS. 


145 


The  shape  of  the  cell  depends  largely  on  the  number  of  processes, 
and  the  manner  in  which  they  come  off  from  the  cell.  If  there  is  but 
one  chief  process  the  cell  is  generally  nearly  spherical.  This  is  the 
case  with  most  of  the  cells  of  the  spinal  ganglia  (fig.  163,  B) ;  in  these 
the  single  process,  after  a  short  course,  divides  into  two  fibres,  which 
pass  the  one  centrally  the  other  peripherally  (fig.  178).  When  there 
are  two  main  processes  from  a  nerve-cell  they  often  go  off  in  opposite 
directions  from  the  cell,  which  is  thus 
rendered  somewhat  spindle-shaped 
(fig.  170),  but  occasionally  they 
emerge  at  the  same  part.  When 
there  are  three  or  more  processes, 
the  cell  becomes  irregularly  angular, 
as  in  the  motor-cells  of  the  spinal 
cord  and  the  pyramidal  cells  of  the 
cerebral  cortex. 

In  some  cases  where  there  appear 
to  be  two  fibres  connected  with  a 
cell,  one  of  them  is  derived  from 
another  nerve-cell  elsewhere,  and  is 
passing  to  end  in  a  ramification 
which  envelops  the  cell-body.  In 
certain  situations  the  ramification 
is  coarse  and  forms  a  calyx-like 
investment  to  the  cell-body :  this 
investment  may  be  so  intimately 
united  to  the  body  of  the  second 
cell  that  it  appears  to  be  rooted  into 
the  external  layer  (fig.  171);  in 
other  places  the  pericellular  fibrils 
are  very  fine  and  form  a  felt-work 
over  the  cell-body  (fig.  172),  the  fibrils  coming  in  contact  with 
the  surface  of  the  cell  and  sometimes  ending  in  small  button-like 
enlargements  or  varicosities. 

In  preparations  made  by  Golgi's  chromate  of  silver  method  the 
nerve  cells  and  their  processes  are  coloured  black  by  a  deposit  of 
reduced  silver,  so  that  the  processes  can  be  traced  for  a  considerable 
distance  from  the  body  of  the  cell,  in  fact  in  many  instances  as  far  as 
their  remotest  ramifications.  It  is  found  by  the  employment  of  this 
method  that  the  axis-cylinder  process  is  not  always  an  unbranched 
process,  as  was  formerly  supposed,  but  that  it  usually,  if  not  invariably, 
1 1  am  indebted  to  Dr.  J.   Turner  for  the  drawing  here  reproduced. 


Fig.  172. — Pericellular  neuro-fibbils 
around  a  large  pyramidal  cell 
of  the  human  cortex  cerebri.  ^ 
Methylene  blue  preparation. 


146 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fig.  173. -a  pyramidal  cell  of  the  cobtex  cerebri  of  the  rabbit.  (Cajal.) 

a,  basal  dendrons  ;  p,  apical  dendron  ramifying  near  surfeoe  ;  e,  axon  ;  c,  its 

collaterals  ;  6,  fibres  of  white  matter  of  biam. 


PROCESSES   OF   NERVE  CELLS. 


147 


Fig.  174. 


-Cell  op  type  II.  of  Golgi,  with  short  axon  ramifying  in  thi 

ADJACENT   GREY   MATTER. 


Fig.  175. — Synaptic  connections  of  sympathetic  cells  from  the 

SUPERIOR   CERVICAL   GANGLION   OF   MAN.       (Cajal.) 

The  cells  (A,  B)  show  well-marked  intracapsular  dendrons.  C,  D,  synapses  between 
dendrons  outside  the  cell-capsules  ;  E,  a  fibre,  which  is  itself  surrounded  by  a  fine  spirally 
wound  fibril,  passing  to  a  cell  and  forming  a  synapse  with  the  cell-dendrons  within  the 
capsule,     a,  a,  axons  ;  b,  c,  d,  e,f,  extra-capsular  dendrons. 


148 


THE   ESSENTIALS   OF   HISTOLOGY. 


gives  off  fine  lateral  branches  (collaterals),  which  themselves  tend  to 
ramify  in  the  adjacent  nerve-substance  (fig.  173).     And  although  the 

main  part  of  the  axis-cylinder  process 
usually  passes  on  and  becomes  part  of  a 
long  medullated  nerve-fibre  (cell  of  type 
I.  of  Golgi,  fig.  173),  this  is  not  always 
the  case,  for  in  another  type  of  nerve-cell 
within  the  nerve-centres  (cell  of  type  II. 
of  Golgi,  fig.  17-i)  the  axis-cylinder  pro- 
cess breaks  up  almost  immediately  into 
an  arborescence.  Moreover,  the  long 
process  of  type  I.  (which  becomes  the 
axis-cylinder  of  a  long  nerve-fibre)  ulti- 
mately ends  in  a  similar  manner,  that 
is  to  say,  in  a  terminal  ramification  or 
arborescence,  as  will  be  seen  in  study- 
ing the  endings  of  nerve-fibres,  and 
the  structure  of  the  central  nervous 
system. 

Neurone  theory.  — Each  nerve-cell  is 
generally  regarded  as  an  anatomically 
independent  element  (nerve-unit,  neurone), 
and  the  connection  of  one  nerve-cell 
with  another  is  believed  to  be  effected 
through  the  medium  of  the  terminal 
arborisations  of  the  dendrons  or  axons. 
Such  arborisations  from  different  cells 
may  interlace  with  one  another  (as  in 
the  olfactory  glomeruli,  in  the  retina, 
and  in  the  sympathetic  ganglia)  (fig. 
175),  or  a  terminal  arborisation  from  one  cell  may  embrace  the 
body  or  the  cell-processes  of  another  cell;  as  with  the  cells  of  the  spinal 
cord  (fig.  176)  and  the  cells  of  the  trapezoid  nucleus  of  the  pons  Varolii 
(fig.  171)  and  in  many  other  places.  The  term  neuro-synapse  may 
be  applied  to  these  modes  of  junction.  By  them  nerve-cells  are 
linked  together  into  long  chains  of  neurones,  the  physiological  path 
being  uninterrupted,  although  the  anatomical  path  is,  as  above  indi- 
cated, believed  to  be  interrupted  at  the  synapses. 


Fig.  176.— Arborisatiox  of  col- 
laterals FROM  THE  POSTERIOR 
ROOT-FIBRES  AROVN'I)  CELLS  IN 
THE    POSTERIOR    HORX    OF    GREY 

MATTER.  (Cajal.) 
A,  fibres  of  posterior  column  derived 
from  posterior  root ;  B,  collaterals  ; 
C,  D,  iiurve-cells  in  gi-ey  matter  sur- 
rounded by  the  arborisations  of  the 
collaterals ;  E,  an  arborisation  shown 
separately. 


The  doctrine  of  the  anatomical  independence  of  the  nerve-cell  is  known  as 
the  "neurone-theory "  (Waldeyer).  It  is  supported  by  the  appearances  of 
chromate  of  silver  preparations  of  nerve-cells.  In  these  the  reduction  of  the 
silver  is  strictly  confined  to  single  cells,  which  become  stained  with  all  their 


NEURONE  THEORY. 


149 


])rocesses  ;  and  these  processes,  wlien  demonstrated  by  this  method,  are  never 
found  in  continuity  either  with  the  processes  or  with  the  bodies  of  other 
nerve-cells.  Moreover  many  of  the  facts  relating  to  nerve-degeneration  can 
be  more  readily  interpreted  by  this  theory  than  by  one  which  assumes  the 
existence  of  direct  continuity  between  the  nerve-units.  But  it  has  been 
.shown  by  Apathy  that  in  annelids  (the  nervous  system  of  which  was 
formerl}'  supposed  to  offer  a  typical  example  of  isolated,  linked  "neurones"), 
the  fibrils  are  in  fact  continuous  from  cell  to  cell  and  are  not  interrupted  at 
the  synapses  ;  it  is  therefore  possible  that  the  same  may  prove  true  for 
vertebrates  also,  in  which  case  the  doctrine  of  independent  units  would 
require  modification.  We  may  at  any  rate  assume  the  truth  of  the 
hypothesis  so  far  as  the  nutrition  of  all  the  processes  of  the  nerve-cell  to 
their  remotest  termination  is  concerned,  independently  of  the  question 
whether  there  is  or  is  not  anatomical  continuity  of  nerve-fibrils  from  one 
unit  to  the  other  ;  for  there  are  many  examples  in  both  animal  and 
plant  cells  of  such  interdependence  by  means  of  fibrils,  combined  with 
trophic  independence. 


STRUCTURE   OF  GANGLIA. 

In  the  ganglia  (fig.  177)  each  nerve-cell  has  a  nucleated  sheath  which 
is  continuous  with  the  neurolemma  of  the  nerve-fibre  with  which  the 


Fig.  177. — Longitudinal  section  through  the  middle  of  a  ganglion  on 

THE    posterior    ROOT    OF    ONE    OF    THE    SACRAL    NERVES    OF    THE    DOG,     AS 
SEEN    UNDER   A    LOW   MAGNIFYING    POWER. 

o,  nerve-root  entering  the  ganglion  ;  h,  fibres  leaving  the  ganglion  to  join  the  mixed 
spinal  nerve  ;  c,  connective-tissue  coat  of  the  ganglion  ;  d,  principal  group  of  nerve- 
cells,  with  fibres  passing  down  from  amongst  the  cells,  to  unite  with  the  longitu- 
dinally coursing  nerve-fibres  by  T-shaped  junctions. 


cell  is  connected.  In  the  spinal  ganglia,  and  in  many  of  the  corre- 
sponding ganglia  on  the  roots  of  the  cranial  nerves  of  mammals  and  of 
most  other  vertebrates,  the  cells  have  only  one  issuing  process,  the 
axis-cylinder  process,  which  soon  acquires  a  medullary  sheath  and  then 
passes  with  a  somewhat  convoluted  course  to  some  little  distance  from 
the  cell-body,  where,  still  within  the  ganglion,  it  divides  into  two,  one 
fibre  passing  to  the  nerve-centre,  and  the  other  towards  the  periphery. 


loO 


THE   ESSENTIALS   OF   HISTOLrXxY, 


The  branching  is  T-shaped  or  Y-shaped,  and  always  occurs  at  a  node 
of  Eanvier  (figs.  178,  179).  The  neuro-fibrils  of  the  central  and 
peripheral  branches  retain  their  individuality  in  the  common  trunk 
and  are  traceable  into  a  neuro-fibril  network  within  the  cell-body. 
These  spinal  ganglion-cells  have,  as  a  rule,  no  dendrons,  but  some  show 


Fig.  i: 


-Two  SPECAL  GAXGLIOS-CELLS,    SHOWING  BIFCECATIOX   OF  THEIB 
XERVE-FIBRE  PBOCES.SES.      (Ranvier.) 


n,  nuclens  of  one  of  the  cells  ;   n,  nuclei  of  capsules;   «",  nuclei  of  Schwann's  sheatli; 
c,  c,  e',  c',  constrictions  of  Ranvier. 


short  dendrons  terminating  in  bulbous  enlargements  (fig.  182)  either 
within  the  cell-capsule  or  immediately  outside  it  (Huber,  Cajal). 

The  origin  of  the  axon  is  not  always  simple,  but  may  be  multiple, 
the  several  parts  forming  at  first  a  plexus  close  to  the  cell,  eventually 
joining  to  produce  a  single  axon.  This  multiple  condition  tends  to 
become  accentuated  with  age  (fig.  183).  The  intracapsular  dendrons 
also  occur  in  sympathetic  ganglia  (Cajal)  (figs.  175,  185). 

Two  chief  types  of  cells  occur  in  the  spinal  ganglia,  one  large  and  clear, 
the  other  small  and  staining  almost  uniformly  dark  (fig.  179).  As  was  first 
shown  bv  Dogiel,  the  cell-body  of  the  spinal  gangliou-cell  is  partially 
Invested  by  the  convolut+^.d  ramifications  of  a  fine  afferent  uerve-fibre, 
derived  either  from  one  of  the  other  cells  of  the  same  ganglion  or  from  a 
cell  in  a  neighbouring  sympathetic  ganglion  (fig.  180).  Similar  afferent 
^bres  forming  pericellular  plexuses  als)  occur  in  the  sympathetic  ganglia 
(fig.  186). 

In  the  sympathetic  ganglia  the  nerA-e-cells  usually  have  several 
dendrons  and  one  axon ;  this  usually  becomes  a  non-medullated  nerve- 


STliUCTUKE   OF  GANGLIA. 


151 


Fig.  179.— TY^^:-^  m-  ckkebko-spinal  ganglion-cells,  from  vagus  ganglion 

OF  CAT.     (Ehrlich's  method.)     (Cajal.) 

A,  B,  large  cells  with  much  convoluted  commenceraent  of  axon  ;  C,  D,  smaller  cells  ; 

E,  F,  smallest  cells,  staining  darkly  and  without  convolutions. 


Fig.  180.— Pericellular  arborisations  in  spinal  ganglion-cells.     (Cajal. 

In  A  the  arborisation  extends  over  the  cell-body  ;  in  B  it  is  limited  to  the  axon. 

a,  b,  c,  d,  afferent  fibre. 


152 


THE   ESSENTIALS  OF   HISTOLOGY. 


Fig.  181. — Diagram  showing  some  of  the  cells  of  a  spinal  ganglion 

AND  THEIR   CONNECTION   WITH   NERVE-FIBRES.      (Dogiel.) 

a,  p,  anterior  and  posterior  root  of  spinal  nerve  ;  n,  an  issuing  nerve  bundle ;  sy,  fibres 
from  sympathetic  ;  x ,  a  cell,  the  axon  of  which  ends  in  ramifications  around  the 
cell-bodies  of  the  ordinary  ganglion-cells. 


Fig.  182. — Cerebro-spinal  ganglion-cells,  man.     (Cajal.) 
o,  6,  intracapsular  dendrons,  with  knobbed  extremities. 


SYMPATHETIC  GANGLIA. 


15^ 


ribre,  but  is  occasionally  liiiely  medullatcd.  In  certain  animals  (rabbit, 
hare,  guinea-pig)  the  sympathetic  cells  have  each  two  nuclei  (fig.  184). 
In  the  frog  they  are  unipolar,  but  sometimes  with  a  second  spiral  fibre 
winding  round  the  issuing  axon. 


■J  -^  •._■;■.  ^ ,  -^  - 


Fig.  183. — Senile  type  of  cerebro-spinal  ganglion-cell.     (Cajal.) 
o,  issuing  axon  ;  b,  part  of  pericellular  plexus  ;  c,  pericellular  loops. 


Fig.  184. — A  sympathetic  nerve-cell.     (Ranvier.) 
nn,  nuclei  of  cell ;  /,/,  pale  fibres  issuing  from  cell ;  n',  )i",  nuclei  on  fibres. 


The  cells  of  ganglia  are  disposed  in  aggregations  of  different  size, 
separated   by  the   bundles  of  nerve-fibres  which   are   traversing  the 


154 


THE   ESSENTIALS   OF   HISTOLOGY. 


ganglion  (fig.  177).  The  ganglion  if  large  is  inclosed  by  an  investing 
capsule  of  connective  tissue  which  is  continuous  with  the  epineurium 
and  perineurium  of  the  entering  and  issuing  nerve-trunks. 


Fig.  185.— Two  sympathetic  cells,  man.     (Cajal.) 
rt,  a,  axon  ;  6,  c,  intracapsular  deudrons  ;  d,  knob-like  ending  of  an  intracapsular  dendron. 


DEGENERATION  AND  REGENERATION  OF  NERVE-FIBRES  AND 
NERVE-CELLS. 

Since  each  nerve-fibre  is  the  process  of  a  nerve-cell,  when  a  nerve  is 
cut,  the  separated  part  degenerates.  Its  axis-cylinder  becomes  broken  up 
and  disappears,  the  nuclei  of  the  neurolemma  multiply,  and  the  medullary 
sheath  undergoes  a  process  of  disintegration  into  droplets  of  fatty 
substance  which  stain  intensely  like  fat  itself  in  a  mixture  of  bichro- 
mate of  potash  and  osmic  acid  Avhich  does  not  stain  the  medullary 
sheath  of  normal  fibres.  The  change  which  results  in  the  fibres  was 
described  by  A.  Waller  in  1850,  and  is  known  as  Wallerian  degeneration 
(fig  187,  A  to  c).  In  man  and  mammals  these  changes  begin  24  to  48 
hours  after  section  of  the  nerve,  and  proceed  rapidly,  so  that  by  the 


DEGENERATION   OF   NERVE-FIBRES. 


155 


third  day  the  nerve-tibres  cease  to  conduct  impulses.  When  a  peri- 
pheral nerve  is  cut,  all  the  nerve-fibres  distal  to  the  point  of  section 
must  degenerate,  because  all  have  grown  from  and  are  processes  of 
nerve-cells  in  or  near  the  nerve-centre — the  afferent  fibres  from  the 
cells  of  the  ganglion  on  the  posterior  root,  the  efferent  fibres  from  the 
cells  of  the  anterior  horn  of  the  spinal  cord. 


Fig.  186. — Two  cells  from  a  sympathetic  ganglion  of  man  showing  the 

TERMINATION   OF   AFFERENT   FIBRES    WITHIN   THE   CELL-CAPSULE.       (Cajal.) 
A,  large  ;  B,  small  cell,     a,  b,  afferent  fibres  surrounding  a  dendron  and  passing  into  capsule. 


Waller  supposed  that  no  changes  are  produced  centrally  to  the 
injury  when  a  nerve  is  cut,  nor  indeed  is  there  any  obvious  immediate 
alteration  in  the  nerve-fibre  itself  between  the  injury  and  the  cell- 
body,  although  it  is  stated  that  the  fibrils  of  the  axis-cylinder  dis- 
appear for  a  time.  But  it  was  found  by  Nissl  that  degenerative  changes 
occur  in  the  cell-body  of  every  cell,  whether  motor  or  sensory,  the 
axis-cylinder  of  which    has   been    severed. ^      These   changes  become 

^  But  section  of  the  posterior  root-fibres  central  to  the  ganglia  does  not  entail 
<3egeneration  of  the  ganglion  cells  from  which  they  arise.  Nor  does  section  of 
a  spinal  nerve  always  entail  degeneration  of  the  anterior  horn  cells  from  which 
its  motor  filires  arise  (Van  Gehuchten).  Why  these  apparent  exceptions  occur 
is  not  understood. 


156 


THE   ESSENTIALS   OF   HISTOLOGY 


apparent  a  few  days  after  section  of  the  nerve-fibre  and  consist  in 
a  disintegration  of  the  chromatin  granules,  associated  at  first  with 
a  general  swelling  of  the  cell-body  and  nucleus,  which  passes  to  the 
periphery  of  the  cell.  After  a  time  the  disintegrated  chromatic 
substance  becomes  in  great  measure  removed  and  the  cell-body  and 


Fig.  187. — Degexeration  and  regeneration  of  nerve-fibres  in  the  rabbit. 

(Ranvier.) 

A,  part  of  a  uerve-fibre  in  which  degeneration  has  commenced  in  consequence  of  the 
section,  fifty  hours  previously,  of  the  trunk  of  the  nerve  higher  up  ;  ni>/,  medullarj- 
sheath  becoming  broken  up  into  drops  of  myelin  ;  p,  granular  jirotoplasmic  sub- 
stance which  is  replacing  the  myelin  ;  n,  nucleus  ;  g,  neurolemma.  £,  another 
fibre  in  which  degeneration  is  proceeding,  the  nerve  having  been  cut  four  days  pre- 
viously ;  p,  as  before  ;  cw,  axis-cj-linder  partly  broken  up,  and  the  pieces  inclosed  in 
portions  of  myelin,  mu.  C,  more  advanced  stage  of  degeneration,  the  medullary 
sheath  having  almost  disappeared,  and  being  replaced  by  protoplasm,  p,  in  which, 
besides  drops  of  fatty  substance,  /;<,  are  numerous  nuclei,  n",  which  have  resulted 
from  the  division  of  the  single  nucleus  of  the  intemode.  Z>,  commencing  regener- 
ation of  a  nerve-fibre.  Several  small  fibres,  f ,  t",  have  sprouted  from  the  some- 
what bulbous  cut  end,  b,  of  the  original  fibre,  t ;  a,  an  axis-cylinder  which  has  not 
yet  acquii-ed  its  medullary  sheath ;  s,  «",  neurolemma  of  the  original  fibre. 
A,  C,  and  D  are  from  o,smic  preparations;  B,  from  an  alcohol  and  carmine  pre- 
paration. 


nucleus  become  shrunken  in  volume.     This  process  of  disintegration 
and  disappearance  of  chromatin  may  be  termed  AHssl  degeneration :  it 


DEGENERATION    OF   NERVE-FIBRES.  157 

is  also  known  as  chromatoli/sis.  It  is  brought  about  not  only  by 
section  of  the  axon,  but  also  as  the  result  of  excessive  fatigue  of 
the  intact  cell  (fig.  164),  and  of  the  action  of  a  large  number  of 
drugs  and  poisons. 

The  chromatolysis  may  be  persistent  or  may  be  recovered  from. 
Sometimes  it  is  followed  by  almost  complete  atrophy  of  the  cell- 
body,  and  when  this  is  marked  there  may  be  a  secondary  Wallerian 
degeneration  of  the  part  of  the  nerve-fibre  still  attached  to  the  cell. 
The  chromatolysis  is  accompanied  by  changes  in  the  neurofibrils 
of  the  cells,  which  stain  differently  and  become  granular  (Marinesco). 

Regeneration. — After  a  certain  lapse  of  time,  especially  if  the  cut 
ends  of  the  nerve  are  in  apposition,  continuity  between  them  may 
become  re-established.  But  when  such  regeneration  takes  place  in 
the  cut  nerve,  it  is  effected  not  by  a  re-establishment  of  connection 
between  the  degenerated  fibres  and  the  fibres  of  the  central  stump, 
but  by  an  outgrowth  of  new  fibres  from  the  stump  (figs.  187,  D;  188), 
which  endeavour  to  find  their  way  to  the  periphery  along  the  course 
of  the  degenerated  fibres.  If  they  succeed  in  doing  so,  the  continuity 
and  conducting  power  of  the  nerve  become  ultimately  restored.  This 
may  not  happen  for  three  months  or  more,  according  to  the  length 
of  nerve  cut  off  and  the  nature  of  the  severance,  although  the  process 
begins  within  a  few  days  of  the  injury  in  man.  Some  investigators 
have  attempted  to  show  that  regeneration  may  take  place  independently 
in  the  peripheral  part  of  the  cut  nerve,  but  the  evidence  oflfered  is 
not  conclusive,  although  changes  occur  in  the  peripheral  part  pre- 
paratory to  the  down-growth  of  new  fibres  into  it  (Mott,  Halliburton 
-and  Edmunds).  There  appears,  however,  to  be  no  union  of  the  down- 
growing  fibres  with  regenerated  fibres  in  the  peripheral  part.  The  recent 
investigations  of  Cajal  have  shown  conclusively  that  whenever  con- 
tinuity is  re-established  it  is  invariably  due  to  the  growth  of  fibres  from 
the  central  stump  of  the  cut  nerve.  These  down-growing  fibres 
are  usually  terminated  by  a  button-like  swelling  similar  to  that  which 
characterises  the  growing  fibres  of  the  embryonic  nerves  (incremental 
■cone),  and  they  may  also  exhibit  numerous  lateral  ramifications  (figs. 
188,  189).  Even  when  the  cut  central  stump  is  turned  backwards 
and  fixed  amongst  the  muscles  or  under  the  skin  a  certain  number 
of  newly-budded  fibres  may  find  their  way  from  it  into  the  degenerated 
peripheral  part  of  the  nerve. 

If  regeneration  fail  to  establish  itself,  the  central  end  of  the  cut 
fibre  and  the  cell-body  from  which  it  takes  origin  undergo  slow 
atrophic  changes  resulting  from  disuse.  These  atrophic  changes  may 
ultimately    extend   to   other   links    in    the    cell-chain,    so   that   even 


158 


THE   ESSENTIALS   OF   HISTOLOGY. 


remote  cells  in  the  same  physiological  path  may  eventually  become 
atrophied  {Guddevh  atrophy). 


a 


e  ^1 


.ii^y 


Fig.  188.— Fibres  from  the  central 
CUT    end    ok    sciatic     nerve    (of 

YOUNG    KABBIT)    CUT    10    DAYS    BEFORE 

DEATH.     (Cajal.) 

A,  fibi-cs  showing  down-gi'owth  of  axis-cylin- 
ders (6)  which  are  hivested  by  flattened 
nucleated  cells  ;  <i,  intact  part  still  my- 
elinated. B,  a  fibre,  the  axis-cylinder 
of  which  has  not  gi-own  down  with  the 
rest,  but  which  shows  various  degenerative 
appearances,  such  as  buds  from  the  axis- 
cylinder  and  at  (/,  a  separation  of  tlie  fibrils. 


Fig.  189.— From  the  peripheral  end 

OF  a  nerve  cut  78  DAYS  BEFORE 
DEATH.   (Oajal.) 

n,  c,  enlai-god  growing  ends  of  axis-cylinder 
'  sjirouts  which  have  grown  down  from  the 
central  cut  end  into  the  old  sheaths  of  the 
out  nerve-fibres  (myelin  drops  are  still 
visible  within  the  sheaths).  The  middle 
fibres  (h)  are  interstitial  (not  in  old  sheaths), 
they  show  a  new  formation  of  a  nucleated 
sheath.  The  fibre  d  has  an  enlarged  end, 
n,  with  sheath  h ;  e,  very  fine  fibres  within 
an  old  sheath  ;  to  the  left  of  it,  an  old 
sheath  without  nerve-fibres. 


REGENERATION. 


15^ 


No  regeneration  of  cut  nerve-fibres  ever  occurs  in  the  brain  or 
spinal  cord,  although  the  process  of  degeneration  of  fibres  which 
are  cut  off  from  their  cell-bodies  occurs  in  the  same  manner  as 
at  the  periphery,  and  the  Nissl  degeneration  also  takes  place  in  the 
cell-bodies.  Both  in  the  nerve-centres  and  in  the  peripheral  nerves  (if 
regeneration  fail  to  occur),  the  place  of  the  degenerated  nerve-fibres 
becomes  eventuallv  occupied  by  strands  of  fine  fibres,  somewhat  similar 
to  the  fibres  of  cicatricial  tissue.  These  strands  stain  deeply  with 
carmine  and  remani  unstained  by  osmic  acid  and  by  the  Weigert-Pal 
method,  and  are  thus  differentiated  from  the  surrounding  normal 
medullated  nerves. 

NEUROGLIA. 

In  the  brain  and  spinal  cord  the  nerve-cells  and  nerve-fibres  are 
supported  by  a  peculiar  tissue  which  has  been  termed  the  neuroglia. 
It  is  composed  of  cells  and  fibres,  the  latter  being  prolonged  from  and 


Fig.  190. — Section  of  spixal  cord  of  embryo  chick,  showing  neuroglia 
fibres  prolonged  from  the  epithelium  op  the  central  canal.    (cajal.) 

d,  dorsal ;  v,  ventral  surface  ;  c,  centi-al  canal  from  which  the  neviroglia  cells  and  fibres 
are  seen  to  radiate  to  the  periphery  of  the  cord.  Some  detached  neui-ogUa  cells  are 
also  represented. 


through  the  cells.  Of  the  fibres  some  are  radially  disposed.  These 
start  partly  from  the  lining  layer  of  the  central  canal  of  the  spinal 
cord  and  the  ventricles  of  the  brain,  where  they  are  originally  if 
not  permanently  continuous   with  the  ciliated  epithelium  cells  lining 


160 


THE   ESSENTIALS   OF   HISTOLOGY 


Fig.  191.— Nkuroglia  cells  of  the  cerebellum.    Golgi  method.    (G.  Retzius.) 

a  cells  with  long  parallel  processes  extending  to  surface ;  b,  arborescent  cells ; 
'  c,  "spider"  cells. 


nf:uroglta. 


161 


these  cavities.  They  course  in  a  radial  direction,  slightly  diverging 
as  they  proceed,  and  constantly  branching,  towards  the  surface 
of  the  organ,  where  they  end  in  enlargements  attached  to  the 
pia  mater  (fig.  191,  a).  The  radial  neuroglia  cells  and  fibres  are 
best  seen  in  the  embryo  before  the 
nervous  elements  are  fully  developed 
(fig.  190);  when  first  distinct  they 
are  termed  spongioblasts  (His). 

Other  neuroglia-fibres  are  prolonga- 
tions or  cell-processes  of  branching 
ncuroglia-cells  (glia-cells).  The  cells 
are  stellate  in  shape  (fig.  192),  and 
their  fine  processes  pass  as  neuroglia- 
fibres  between  the  nerve-cells  and 
nerve-fibres,  which  they  aid  in  sup- 
porting. There  appear  to  be  two 
kinds  of  these  neuroglia-cells  differing 
from  one  another  in  the  character  of 
their  processes  (Andriezen).  In  the 
one  kind  the  processes  branch  re- 
peatedly {arbonscent  cells)  (fig.  191,  b) ;  in  the  other  kind  they  remain 
unbranched  from  their  origin  in  the  cell-body  to  their  termination 
{spider-cells)  (fig.  191,  c). 

Some  authorities  {e.g.  Weigert)  have  thought  that  the  fibres  of  the 
neuroglia  are  inter-  not  intra-cellular,  although  it  is  admitted  by  all  that 
they  are  formed  originally  by  the  neuroglia-celLs. 


Fig.  192. — Neuroglia  cell  fkom 
SPINAL  CORD.     (Ranvier.) 

Isolated  after  maceration  in  33  p.c.  alcohol. 


DEVELOPMENT   OF   NERVE-CELLS   AND   NERVE-FIBRES. 

All  nerve-cells  in  the  body  are  developed  from  the  cells  of  the  neural 
groove  and  neural  crest  of  the  early  embryo  ;  the  neural  groove  closing 
to  form  the  neural  canal  (fig.  193),  the  cells  of  which  form  the  spinal 
cord  and  brain,  and  the  neural  crest  giving  off"  at  intervals  sprouts 
which  become  the  germs  of  the  spinal  ganglia.  The  cells  which  line 
the  neural  canal  are  at  first  all  long  columnar  cells,  but  amongst  these, 
and  probably  produced  by  cell-division  from  some  of  these  (fig.  194,  g), 
rounded  cells  {neurublads)  make  their  appearance,  the  remaining 
elongated  cells  forming  the  spongioblasts.  Soon  from  each  neuroblast 
a  process  begins  to  grow  out  (fig.  194,  n,  and  fig.  195).  This  is 
the  axon,  and  it  is  soon  characterised  by  an  enlarged  extremity 
{incremental  cone)  (fig.  196,  h,  h  ;  fig.  197,  B,  e).  As  it  grows,  it  may 
emerge  from  the  antero-lateral  region  of  the  canal  and  become  the 
axis-cylinder  of  a  motor  nerve  or  anterioi'  root-fibre.     The  dendrons  of 

L 


162 


THE   ESSENTIALS   OF   HISTOLOGY. 


the  cell  appear  somewhat  later  than  the  axon.  The  axis-cylinder 
processes  of  some  of  the  neuroblasts  remain  within  the  nerve-centre^ 
and  are  developed  into  commissural,  association,  and  intercentral 
fibres. 


A. 


Fig.  193.— Closure  of  neural  c.\nal  of  human  embryo,  showing  the  cells 
OF  the  neural  crest  becoming  separated  to  form  the  germs  of  the: 
SPINAL  ganglia.     (Lenliossek. ) 

A,  canal  still  opon  ;   B,  canal  closed. 


Fig.  194. 


Fig.  19.5. 


Fig.  194.— Section  of  neural  epithelium  of  early  embryo.     (His.) 
Highly  magnified  view  of  jiart  of  a  section,  at  the  time  of  the  first  differentiation  of 
the  neuroblasts,  .showing,  s',  spongework  formed  of  the  outer  ends  of  columnar 
epithelium  cells,  s  ;  g,  rounded  "  germinal  cells  "  in  process  of  division  (probably 
to  form  neuroblasts) ;  n,  a  neuroblast. 

Fig.  195.— Neuroblasts  from  a  pig-embryo,  showing  three  stages  of 
development.     (Gurwitsch,  after  Scott.)     (Highl3' magnified.) 

The  sprouts  from  the  neural  crest  contain  the  neuroblasts  from  which 
the  posterior  root-fibres  are  developed.  Axons  grow  out  from  these 
neuroblasts  in  two  directions,  so  that  the  cells  become  bipolar  (fig.  198). 


DEVELOPMENT   OF   NERVE-CELLS. 


163 


One  set  of  processes,  forniin^c  the  posterior  root-fibres,  grow  into  the 
postero-lateral  portion  of  the  spinal  cord  and  ramify  in  the  developing 
grey  matter ;  the  other  set,  containing  the  afferent  fibres  of  the  spinal 
nerves,  grow  towards  the  developing  anterior  roots,  and  eventually 
mingle  with  them  to  form  the  mixed  nerves.  As  development  pro- 
ceeds, the  bipolar  ganglion  cells  become  gradually  transformed  in  most 


Fig.  196. 


fa 


Fig.  197. 

Fig.  196. — Section  of  spixal  cord  of  chick  of  third  d.\y  of  incubation. 

(Cajal. ) 

A,  anterior  root-fibres  formed  by  outgrowths  of  motor  neuroblasts,  c,  c  ;  B,  posterior 
root-fibres  formed  by  ingrowths  of  bipolar  sensory  neuroblasts,  o,  in  ganglion  rudi- 
ment ;  a,  early  neuroblasts ;  b,  neuroblast  giving  rise  to  a  commissural  nerve-fibre, 
d  ;  h,  i,  enlarged  ends  of  growing  axons  ;  e,  t,  neuroblasts  of  which  the  dendrons 
are  beginning  to  appear. 

Fig.  197. — Neuroblasts  from  the  spinal  cord  of  a  third-day  chick 

EMBRYO.     (Cajal.) 
A,  three  neuroblasts,  stained  by  Cajal's  reduced  silver  method,  showing  a  network  of 

neuro-fibrils  in  the  cell-body  ;  a,  a  bipolar  cell.     B,  a  neuroblast  stained  by  the 

method  of  Golgi,  showing  the  incremental  cone,  c. 


vertebrates,  by  a  shifting  of  the  two  axons,  into  unipolar  cells  (fig. 
198,  h,  i,  j  ;  fig.  199) ;  but  in  some  fishes  the  cells  remain  permanently 
bipolar  (fig.  170).  This  is  also  the  case  with  the  ganglion-cells  of  the 
eighth  cranial  nerve  (ganglion  of  Scarpa  and  ganglion  of  the  cochlea). 

The  ganglia  on  the  sympathetic  and  on  other  peripheral  nerves  are 
developed  from  small  masses  of  neuroblast-cells  which  separate  off 
from  the  germs  of  the  spinal  ganglia  and  give  origin  to  axons 
and  dendrons  much  in  the  same  way  as  do  the  neuroblasts  within 
the  central  nervous  svstem. 


164 


THE   ESSENTIALS   OF  HISTOLOGY, 


The  manner  in  which  the  medullary  sheath  and  neurolemma  of 
the  nerve-fibres  are  formed  is  not  well  understood.  It  is  usually- 
assumed  that  they  are  also  ectodermic  in  origin  and   are  developed 


Fig  198.— Spinal  and  sympathetic  ganglia  and  part  of  spinal  cord  of 

CHICK  of  seventeenth  DAY  OF  INCUBATION.   (Cajal.) 

a,  autero-lateral  part  of  spinal  cord  with  d,  a  motor  nerve-cell ;  the  fibres  of  the  anterior 
root  are  seen  emerging  and  passing  to  B  (the  connection  appears  interrupted 
in  the  section) ;  C,  posterior  root  formed  of  fibres  which  have  grown  from  the 
ganglion-cells  in  D,  spinal  ganglion ;  B,  mixed  spinal  nerve ;  F,  sympathetic 
ganglion  ;  a,  a,  axons  of  sympathetic  cells,  passing  to  join  the  spinal  nerve  ;  b,  dcn- 
drons  of  these  cells ;  c,  axons  passing  to  the  sj'mpathctic  cord ;  h,  cells  of  spinal 
ganglion  still  bi]wlar ;  i,  i,  bipolar  cells  becoming  transformed  into  unipolar ; 
V,  unipolar  cell  with  T-junction  ;  /,  section  of  an  artery ;  </,  body  of  vertebra. 


Fig.  199. — Spinal  ganglion-cells  showing  transitions  from  bipolar  to 
UNlPOL.\R  CONDITION.     (Holmgren.) 


from  ectoderm  cells  which  grow  out  from  the  embryonic  central 
nervous  system  along  the  axis-cylinder  processes  of  the  neuroblasts. 
But  this  is  by  no  means  clear.     It  is  more  probable  that  the  medullary 


DEVELOPMENT  OF   NERVE-FIBRES.  166 

substance  is  formed  by  the  axis-cylinder  itself,  and  that  the  neurolemma 
with  its  nuclei  is  derived  from  extrinsic  cells,  perhaps  of  mesodermic 
orif^in. 

The  neuroglia-cells  appear  to  be  developed  from  ectoderm  cells 
(spongioblasts)  of  the  wall  of  the  neural  canal,  which,  in  place  of 
giving  ofi"  axon  and  dendrons  like  the  neuroblasts,  send  out  a  number 
of  tine  processes  in  all  directions  from  the  cell  to  form  the  fibres 
of  the  neuroglia.  It  is  held  by  some  authorities  that  the  neuroglia  has 
a  double  origin,  some  of  the  cells  being  developed  from  ectoderm  and 
others  from  mesoderm. 

Some  neurologists  are  of  opinion  that  the  nerve-fibres  do  not  grow  out 
from  single  nerve-cells  in  tlie  manner  above  described,  but  are  formed  of 
chains  of  cells  which  emerge  from  the  neural  ectodeira  or  from  the  ganglion- 
rudiments,  and  join  end  to  end  into  a  syncytium,  which  gradually  lengthens 
out  into  the  nerve-fibre,  the  nuclei  of  the  syncytium  becoming  the  nuclei  of 
the  sheath  of  Schwann,  and  the  protoplasm  of  the  syncytium  becoming 
differentiated  into  axis-cylinder,'  medullary  sheath,  and  neurolemma  as 
development  advances.  Others,  whilst  agreeing  that  the  axis-cylinders 
grow  out  as  cell  processes  from  the  neui^oblasts  of  the  neural  canal  and 
ganglia,  describe  those  outgrowing  processes  as  suri^ounded  by  other  neural 
ectoderm  cells — lemmal  cells — which  accompany  them  in  their  progress 
through  the  tissues,  multiplying  as  they  proceed,  and  forming  eventually 
the  nucleated  sheath  of  Schwann  of  the  medullated  nerve. 


166  THE   ESSENTIALS  OF   HISTOLOGY. 


LESSON    XIX. 
MODES  OF  TERMINATION  OF  NERYE-FIBRES. 

1.  Shell  out  a  Pacinian  coi'jju.scle  from  a  piece  of  cat's  mesentery  either  fresh 
or  after  having  been  kept  for  two  or  three  days  in  ^X5  P^r  cent,  chromic  acid 
or  in  5  per  cent,  formol.  Clear  it  as  much  as  possible  of  adhering  fat,  but  be 
careful  not  to  prick  or  otherwise  injure  the  corpuscle  itself.  Mount  in  water  or 
saline  with  a  thick  hair  to  pn-event  crushing  with  the  cover-glass.  Sketch  the 
corpuscle  under  a  low  power,  and  afterwards  draw  under  a  high  power  the 
part  of  the  core  where  the  nerve  enters  and  the  part  where  it  terminates. 
Notice  the  fibrous  structure  of  the  lamellar  tunics  of  the  corpuscle  and  the 
oval  nuclei  belonging  to  flattened  epithelioid  cells  which  cover  the  tunics. 
The  distinct  lines,  which  when  seen  in  the  fresh  corpuscles  are  generally 
taken  for  the  tunics,  are  really  the  optical  sections  of  these  flattened  cells. 

Pacinian  corpuscles  may  be  observed  in  sections  of  skin  ;  tactile  corpuscles 
and  end-bulbs  may  also  be  seen  in  certain  parts  of  the  integument. 

2.  Study  the  corpuscles  of  Grandry  and  of  Herbst  in  sections  of  the  skin 
covering  the  duck's  bill. 

3.  Mount  in  dilute  glycerine  sections  of  a  rabbit's  cornea  which  has  been 
stained  with  chloride  of  gold  by  Klein's  methocL  Notice  the  arrangement  in 
plexuses  of  the  darkly-stained  nerve-fibres  and  fibrils,  (1)  in  the  connective- 
tissue  .substance,  (2)  under  the  epithelium,  and  (3)  between  the  epithelial 
cells.     Make  one  or  two  sketches  showing  the  arrangement  of  the  fibrils. 

4.  Spread  out  a  small  piece  of  muscle  which  has  been  stained  with  chloride 
of  gold  by  LiJwit's  method,  or  with  htematoxylin  by  Sihler's  method,  and 
examine  it  with  a  low  power  to  find  the  nerve-fibres  cros.sing  the  muscular 
fibres  and  distributed  to  them. 

The  pieces  of  muscle  may  advantageously  be  thinned  out  for  observation 
by  pressure  upon  the  cover-glass.  Search  thoroughly  for  the  close  terminal 
ramifications  (end-plates)  of  the  axis-cylinders  immediately  within  the  sar- 
colemma. 

These  nerve-endings  as  well  as  others  elsewhere  can  also  be  displayed  in 
preparations  made  by  Ehrlich's,  Golgi's  or  Cajal's  methods  (see  Appendix). 


Modes  of  ending  of  sensory  nerve-fibres. — Xerve-fibres  which  are 
distributed  to  sensory  parts  end  either  in  special  organs  or  in  free 
terminal  ramijications,  these  last  being  usually  in  epithelia.  "Within 
the  special  organs  the  actual  nerve-ending  is  also  generally  ramified. 

Nerve-endings  in  special  connective-tissue  organs. — Three  chief 
kinds  of  these  special  organs  are  usually  described,  represented  in 
man  by  Pacinian  corpuscles,  tactile  corpuscles,  and  end-hulbs.  The  type  is 
the  same  in  all :  a  lamellated  connective-tissue  capsule  enclosing  a  core 
of  a  soft  material  which  appears  to  be  composed  of  nucleated  proto- 
plasmic cells ;  the  capsule  being  an  expansion  of  the  perineurium,  and 
the  core  of  the  endoneurium  of  the  nerve.     Within  the  core  the  axis- 


ENDING   OF   NERVE- FIBRES. 


167 


cylinder  terminates  either  simply  or  by  a  more  or  less  complex 
arborescence.  The  variations  which  occur  are  chieHy  due  to  the 
complexit}^  of  the  capsule,  which  is  simplest  in  the  end-bull)s  and 
most  complex  in  the  Pacinian  corpuscles.     In  the  tactile  corpuscles 


Fig.    200. 


Fig.  201. 
Fig.  200.— Tactile  corpuscle  within  a  papilla  of  the  skin  of  the  hand. 

STAINED   with    CHLORIDE   OP   GOLD.       (Ranvier. ) 
n,  two  nerve-fibres  passing  to  the  corpuscle  ;   a,  a,  varicose  ramifications  of  the  axis- 
cylinders  within  the  corpuscle. 


Fig.  201. 


-End-bulbs  at  the  termin.\tions  of  nerves  in  the  human  con- 
junctiva, AS  seen  with  a  lens.     (Lougworth.) 


Fig.  202.— a  medullated  fibre  terminating  in  several  end-bulbs  in  the 
HUMAN  peritoneum.     (Dogiel.)     Methylene  blue  preparation.     Low  power. 


168 


THE   ESSENTIALS   OF  HISTOLOGY. 


and  end-bulbs  the  connective-tissue  sheath  of  the  medullated  fibre 
expands  to  form  a  bulbous  enlargement,  which  is  cylindrical  or 
spheroidal  in  the  end-bulbs  and  ellipsoidal  in  the  tactile  corpuscles. 
In  both  Jcinds  of  end-organ  as  the  nerve-fibre  enters  (which  in  the 
tactile  corpuscle  only  happens  when  it  has  reached  the  distal  part, 


Fig.  203. — End-bulbs  from  the  human  peritoneum.     (Dogiel.)    More  highl}' 

magnified.     Methylene  blue  preparation. 

o,  medullated  fibre  ;  b,  nucleated  lamellated  capsule  of  end-bulb  ;  c,  non-taeduUated  fibres, 

probably  destined  for  the  capillaries  which  surround  the  end-bulbs. 


Fig.  204. — End-bulb  from  the  centr.\l  tendon  of  the  diaphr.\gm  of  the  dog. 
(Dogiel.)  Showing  besides  the  main  medullated  fibre  terminating  by  an 
arhorescence  within  the  core,  a  second  ver3'  fine  medullated  fibre,  forming  a 
more  delicate  arborescence  around  the  ending  of  the  main  fibre  in  the  outer 
part  of  the  core.     Methylene  blue  preparation. 

after  having  wound  spirally  once  or  twice  round  the  corpuscle)  it 
loses  its  sheaths  and  is  prolonged  as  an  axis-cylinder  only  ;  this  gene- 
rally ramifies  and  its  branches  terminate  after  either  a  straight  or 
a  convoluted  course  within  the  organ ;  but  it  sometimes  remains 
almost  unbranched  (see  figs.  200  to  205).  Tactile  corpuscles  occur 
in  some  of  the  papillae  of  the  skin  of  the  hand  and  foot,  in  sections 
of  which  they  can  be  studied  (see  fig.  277).  End-bulbs  are  found 
in  the  conjunctiva  of  the  eye,  where  in  most  animals  they  have  a 
cylindrical  or  oblong  shape,  but  in  man  they  are  spheroidal  (fig.  201). 


ENDING   OP   N KRVE-FIBRES. 


169 


They  have  also  been  t'ouiul  in  paj)illa'  of  the  lips  and  tongue,  in 
serous  membranes,  in  tendons  and  aponeuroses,  and  in  the  epineurium 
of  the  nerve-trunks ;  and  somewhat  similar  sensory  end-organs 
{(jenital  rorpasflcs)  also  occur  in  the  integument  of  the  external  genital 
organs  of  both  sexes  (fig.  205).  Similar  bodies  of  larger  size  are 
also  met  with  in  the  neighbourhood  of  the  joints  {articular  corpuscles). 
In  the  skin  covering  the  bills  of  certain  birds  {e.g.  duck),  a  simple  form 
of  end-organ  {corpuscle  of  Gravdri/,  fig.  206)  occurs,  consisting  of  two 
or  more  cells  arranged  in  rows  within  a  capsule,  with  the  axis-cylinder 
terminating  in  flattened  expansions  {tactile  dish)  between  the  cells. 


Fig.  206. — Tactilk  corpuscles  from  the 

duck's  tongue.     (Izquierdo.) 
A,  composed  of  three   cells,  with   two  inter- 
posed disks,  into  which  the  axis-cylinder  of 
the  nerve,  n,  is  observed  to  pass  ;  in  B  there 
is  but  one  tactile  disk  inclosed  between  two 
Fig.   205.— End- bulb    from    the  glans  tactile  cells. 

PENIS,  SHOWING  ENDING  OF  AXIS-CYLIN- 
DER.    Methylene  blue  preparation. 
(Dogiel.) 
a,  medullated  nerve-fibre ;  6,  sheath  of  end-bulb. 

The  Pacinian  corpuscles  are  larger,  and  have  a  more  complex 
structure,  than  the  tactile  corpuscles  and  end-bulbs  (fig.  207).  They 
are  composed  of  a  number  of  concentric  coats  arranged  like  the  layers 
of  an  onion,  and  inclosing  the  prolonged  end  of  a  nerve-fibre.  A  single 
medullated  nerve-fibre  goes  to  each  Pacinian  corpuscle,  encircled  by 
a  prolongation  of  the  perineurium  {sheath  of  Henle),  and  within  this  by 
endoneurium ;  when  it  reaches  the  corpuscle,  of  which  it  appears 
to  form  the  stalk,  the  lamellae  of  the  perineurium  expand  into  the 
tunics  of  the  capsule.  The  nerve  passes  on,  piercing  the  tunics,  sur- 
rounded by  endoneurium,  and  still  provided  with  medullary  sheath,  to 
reach  the  central  part  of  the  corpuscle.  Here  the  endoneurium  is 
prolonged  to  form  a  core  of  cylindrical  shape,  along  the  middle  of 
which  the  nerve-fibre,  now  deprived  of  its  medullary  and  primitive 
sheaths,   passes  in  a  straight  course  as  a  simple  axis-cylinder  (tigs. 


170 


THE   ESSENTIALS  OF  HISTOLOGY. 


207,  n' ;  208,  c.f)  to  terminate  at  the  farther  end  of  the  core,  either  in 
an  arborisation  or  in  a  bulbous  enlargement.  In  its  course  through 
the  core  it  may  give  off  lateral  ramifications,  which  penetrate  to  all 
parts  of  the  core,  and  themselves  end  in  fine  branches. 


Fig.  207. — Magnified  view  of  a  pacinian  body  from  the  cat's  mesentery. 

(Ranvier.) 

n,  stalk  of  corpuscle  with  nerve-fibre,  inclosed  in  sheath  of  Henle,  passing  to  the 
corpuscle ;  n',  its  continuation  through  the  core,  in,  as  axis-cylinder  only  ;  a,  its 
terminal  arborisation  ;  c,  d,  sections  of  epithelioid  cells  of  tunics,  often  mistaken  for 
the  tunics  themselves ;  /,  channel  through  the  tunics  which  expands  into  the  core  of 
the  corpuscle. 


PACINIAN  CORPUSCLES. 


171 


Besides  the  medullated  fibre,  which  is  always  very  conspicuous,  it  has  been 
shown  that  both  the  Pacinian  and  Herbst  corpuscles  receive  in  addition  a 
fine  non-meilullated  nerve-fibre,  which  arborizes  over  the  outer  surface  of  the 
core.  A  similar  arranf^euient  also  obtains  in  Granilry's  corpuscles,  where  the 
tactile  cells  are  surrounded  with  such  an  arborization  (Dogiel  and  others). 

The  tunics  of  the  capsule  are  composed  of  connective  tissue,  the 
fibres  of  which  for  the  most  part  run  circularly.     They  are  covered 


Fig.  209. 

Fig.  208.— Part  of  pacinian  body,  showing  the  nerve-fibre  entering 
THE  core.      From  an  osiiic  acid  preparation. 

ms,  entering  nerve-fibre,  the  medullary  sheath  of  which  is  stained  darkly,  and  ends 
abruptly  at  the  core,  c ;  i>s,  prolongation  of  primitive  sheath  or  neurolemma 
passing  towards  the  outer  part  of  the  core ;  c.f,  axis-cylinder  passing  through 
the  core  as  the  central  fibre ;  •=,  some  of  the  inner  tunics  of  the  corpuscle,  en- 
larged where  the\-  abut  against  the  canal  through  which  the  nerve-fibre  passes 
— the  dots  within  them  are  sections  of  the  fibres  of  which  they  are  composed ; 
n,  nuclei  of  the  tunics ;  »>.',  nuclei  of  the  endoneuriuni-cells,  continued  by  others 
in  the  outer  part  of  the  core. 


Fig.  209. 


-Pacinian  corpuscle  from  the  cat,  stained  with 

SILVER  nitrate. 


on  both  surfaces  with  a  layer  of  flattened  epithelioid  cells  (fig.  209), 
and  here  and  there  cleft-like  lymph-spaces  can  be  seen  between  them 
like  those  between  the  layers  of  the  perineurium. 

Pacinian  corpuscles  occur  in  many  parts,  e.g.  in  the  deeper  layers  of 
the  skin  of  the  hands  and  feet,  in  the  periosteum  of  some  bones,  in 
the  neighbourhood  of  tendons  and  ligaments,  in  the  connective  tissue 


172 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fig.  210. — Section  of  pacinian  corpuscle.     (Szymonowicz.) 

f ,  one  of  the  layers  of  epithelioid  colls  ;  n,  nucleus  of  epithelioid  cell.  It  is  seen  that  the 
tunics  are  very  closely  packed  around  the  core,  in  the  middle  of  which  the  axial-flbro 
is  cut  across. 


.^^^^'^^^H,- 


•^ 


Fig.  211.— Herbst  corpuscle  of  duck.     (Sobotta.)     x380. 

11,  nieduUated  nerve-fibre  ;  a,  its  axis-cylinder,  terminating  in  an  enlargement  at  end 
of  core  ;   c,  nuclei  of  cells  of  core  ;  t,  nuclei  of  cells  of  outer  tunics  ;  t',  inner  tunics. 


PAC;iNIAN   CORPUSCLES. 


173 


at  the  back  of  the  abdomen,  oiid  (in  the  cat)  very  numerously  in  the 
mesentery,  where  they  are  most  easily  got  for  observation, 

A  simple  form  of  Pacinian  corpuscle  with  fewer  tunics  and  a  core  formed 
of  regularly  arranged  cells  occurs  iu  birds  {roi-pusclea  of  Herhst,  fig.  211). 

Although  most  of  the  nerve  endings  in  connective-tissue  structures 
are  enclosed  within  lamellated  capsules,  nerves  are  found  to  end  in 
some  situations  in  arborisations  between  the  bundles  of  connective- 
tissue  fibres.    This  has  been  shown  by  Dogiel  to  occur  in  intermuscular 


Fig.  212.— TERnriNAL  arborisation  from  the  intermuscular  co.nnective 

TISSUE   OF   THE    RECTUS   ABDOMINIS    OF    THE    RABBIT.      METHYLENE   BLUE 

preparation.     (Dogiel.) 


,-j*^^^^ 


Fig.  213. — Terminal  arborisation  from  the  superficial  layer  of  the 
peritoneum  of  the  rabbit.  Methylene  blue  preparation.  (Dogiel.) 

a,  medullated  fibre  ;  b,  fibre  connecting  the  arborisation  with  another  one 
not  here  represented. 


connective-tissue  septa  (fig.  212);  and  in  serous  membranes  (fig.  213); 
in  the  latter  such  arborisations  may  be  quite  superficial  and  placed  just 
below  the  endothelium. 

Organs  of  Ruffini. — These,  which  resemble  long  cylindrical  end-bulbs, 
are  composed  of  connective-tissue  bundles,  within  which  the  axis- 
cylinders  of  the  nerves  ramify,  and  end  in  flattened  expansions.     They 


174  THE   ESSENTIALS   OF   HISTOLOGY. 

occur  commonly  in  the  subcutaneous  tissue  of  the  human  finger  (fig. 
214).  Other  encl-bulb-like  organs,  spheroidal,  oval,  or  cylindrical  in 
form,  have  been  described  by  Ruffini  under  the  name  of  Golgi-Mazzoni 
corpuscles ;  they  appear  to  be  varieties  of  the  ordinary  end-bulb 
of  W.  Krause.  They  occur  in  tendons  and  in  the  subcutaneous  tissue 
of  the  pulp  of  the  finger. 


Fig.  214. — A  nerve  fibre  is  shown  dividing  into  seven  secondary  fibres 
TO  WHICH  are  attached  FIVE  ORGANS  OF  RUFFINI.    (Barker,  after  RufEni. ) 

Organs  of  Golgi. — A  special  mode  of  nerve-ending  is  met  with  in 
many  tendons,  near  the  points  of  attachment  of  the  muscular  fibres. 
The  tendon-bundles  become  somewhat  enlarged  and  split  into  a 
number  of  smaller  fasciculi,  and  the  nerve-fibres — one,  two,  or  even 
more  in  number — pass  to  the  enlarged  part,  and  penetrating  between 
the  fasciculi  of  the  tendon  lose  their  medullary  sheaths,  while  the  axis- 
cylinders  end  in  a  terminal  arborisation,  beset  with  irregular  vari- 
cosities. The  structure  (fig.  215)  is  enclosed  within  a  fibrous  capsule 
continuous  with  the  areolar  tissue  covering  the  bundles  of  the  tendon  ; 
and  between  the  capsule  and  the  organ  proper  is  a  lymph-space, 
similar  to  that  which  is  found  in  the  muscle-spindle  (see  p.   179). 

Free  nerve -endings. — When  sensory  nerve-fibres  terminate  in  epi- 
thelium, they  generally  branch  once  or  twice  in  the  subepithelial 
connective  tissue  on  nearing  their  termination.  The  sheaths  of  the 
fibres  then  successively  become  lost,  first  the  connective  tissue  or 
perineural  sheath,  then  the  medullary  sheath,  and  lastly  the  neuro- 
lemma, the  axis-cylinder  being  alone  continued  as  a  bundle  of  primitive 
fibrils  (fig.  216).  This  branches,  and  with  the  ramifications  of  the 
axis-cylinders  of  neighbouring  nerve-fibres  forms   a  primary  plexus. 


FREE   NERVE-ENDINGS. 


175 


Fig.  215. — Organ  of  golgi  from  the  human  tendo  achillis.     Chloride 

OF   GOLD   PREPARATION.       (Ciaccio.) 

m,  muscular  fibres  ;  t,  tendon-bundles  ;  G,  Golgi's  organ  ;  n,  two  nerve-fibres  passing  to  it. 


Fig.  216. — Plexus  of  nerve  fibres  in  the  rabbit's  cornea  : 

Methylene  blue.     (Cajal.) 

A,  trabecula  of  primary  plexus  ;  B,  secondary  plexus  ;  C,  intraepithelial  fibrils. 


176 


THE   ESSENTIALS   OF  HISTOLOGY. 


From  the  primary  plexus  smaller  branches  come  off,  and  these  form 
a  secondary  plexus  nearer  the  surface,  generally  immediately  under 
the  epithelium  if  the  ending  is  in  a  membrane  covered  by  that  tissue. 
Finall}',   from  the   secondary    plexus    nerve-fibrils   proceed   and   form 


Fig.  217. — Vertical  section  of  corxe.\  stained  with  CHLORinE  of  gold. 

(Ranvier. ) 

n,  r,  primary  plexus  In  connective  tissue  of  cornea  ;  o.,  branch  passing  to  subepithelial 
plexus,  s  ;  p,  intraepithelial  plexus  ;  b,  terminatioiis  of  fibrils. 

terminal  ramifications  amongst  the  tissue  cells  (fig.  217,  p,  h),  the 
actual  ending  being  generally  in  free  varicose  fibrils  (h).  This  mode 
of  ending  is  characteristically  seen  in  the  cornea  of  the  eye,  but  can 
also  be  rendered  evident  in  other  epithelia  (fig.  218).     The  fibrillar 


Fig.  218. — Intra-efithelial  nerve-terminations  in  the  larynx: 
GOLGI  method.     (G.  Retzius. ) 

On  the  left  the  epithelium  is  stratified  and  on  the  right  ciliated  columnar. 
/I,  nerve-fibres  in  corium. 

Structure  of  the  ramifications  of  the  axis-cylinders  is  very  apparent 
in  some  of  the  preparations  figured. 

In  some  situations  the  nerve-fibrils  within  a  stratified  epithelium 
terminate  in  flattened  or  crescentic  expansions  which  lie  in  the  inter- 
stices of  the  deeper  epithelium  cells,  to  some  of  which  they  are  applied. 


FREE   NERVE-ENDINGS. 


177 


These  expansions  are  known  as  tactile  disks ;  they  are  character- 
istically developed  in  the  skin  of  the  pig's  snout  (fig.  210),  and  are  also 
found  in  the  outer  root  sheath  of  hairs  and  in  the  deeper  parts  of  the 
epidermis  in  various  parts.  With  appropriate  treatment  it  may  be 
shown  that  they  consist  of  a  fine  network  of  neurofibrils  (fig.  220). 


cc — =-,  ^, — 


Fig.  219.— Ending  of  nerve  in  tactile  disks  in  the  pig's  snoct. 
( Kanvier. ) 

71,  meduUated  fibre  ;  m,  terminal  disks  or  menisci;  e,  cells  of  the  Malpighian  layer  of  the 
epidermis ;  o,  somewhat  modified  cell  to  which  a  tactile  disk  is  applied. 


Fig.  220. — A  nerve-fibre  ending  in  a  number  of  tactile  menisci 
FROM  A  TACTILE  HAIR,  RABBIT.     (C'ajal  and  Telle. ) 

a,  point  of  ramification  of  axis-cylinder  of  nerve-fibre;  B,  isthmus  between  two  menisci ; 
C,  terminal  meniscus ;  D,  large  meniscus  at  branching  of  sevei'al  divisions  of  the 
nerve-ending. 


Sensory  nerves  of  muscles. — The  sensory  nerves  of  muscles  end 
in  peculiar  organs  which  were  termed  by  Kiihne  muscle-spindles. 
Their  structure  has  recently  been  specially  investigated  by   Eutfini, 

M 


178 


THE   ESSENTIALS   OF   HISTOLOGY. 


Huber,    and    Dogiel ;    and    also    by    Sherrington,    who    has    shown 
that  the  large  medullated   nerves   which   they  receive    (about   three 


H 


f*««ii 


Fig.  222. 


Fig.  221. 


Fig.   221.— Nerve-exdixgs  upox  the  intrafusal  mi'scle- 
fibres  of  a  muscle-spindle  of  the  rabbit;  moder.atelt 

MAGNIFIED.  METHYLENE  BLUE  PREPARATION.  (Dogiel.) 
o,  large  medullated  fibre  coming  off  from  • '  spindle  "  nerve  and  passing 
to  end  in  an  annulo-spiral  termination  on  and  between  the  intra- 
f  u.sal  fibres  ;  h,  a  fine  medullated  fibre  coming  off  from  the  same 
stem  and  dividing.  Its  b\-anches,  c,  pass  towards  the  ends  of  the 
muscle-fibres  and  terminate  in  a  number  of  small  localised  arborisa- 
tions, like  end-plates. 

Fig.  222.— An  annulo-spiral  ending  of  intrafusal  fibre; 

HIGHLY     magnified.  METHYLENE     BLUE     PREPARATION. 

(Dogiel.) 


MUSCLE-SPINDLES.  179 

or  four  such   fibres  entering  each  spindle  not  far  from  its  equator), 
are  derived  from  the  posterior  root-ganglia. 

The  muscle-spindle  is  a  fusiform  body,  from  075  to  4  mm.  long, 
and  from  0-OS  to  02  mm.  in  diameter;  it  lies  parallel  with  the 
general  direction  of  the  fibres  of  a  muscle.  It  consists  of  a  lamellated 
connective-tissue  sheath  externally,  within  which  is  a  bundle  (intrafusal 
bundle)  of  from  two  to  twelve  peculiar  muscle-fibres.  These  form  an 
axial  mass  with  some  connective  tissue  and  the  nerve-fibres  ;  between 
this  axial  bundle  and  the  .sheath  is  a  lymphatic  periaxial  space,  bridged 


Fig.  223. — .Sensory  xekve  terminatixg  ix  arborisatioxs  around  the 
ENDS  OF  MUSCLE-FIBRES.     (Cecchcrelli.) 

across  by  filaments  of  connective  tissue.  The  intrafusal  muscle-fibres 
are  somewhat  like  embryonic  fibres  in  appearance,  being  smaller  than 
the  ordinary  fibres  of  the  muscle  and  having  a  relatively  large  number 
of  nuclei  with  surrounding  protoplasm,  as  in  the  red  variety  of  muscle. 
At  the  proximal  end  of  the  spindle  they  are  usually  only  two  or  three 
in  number,  but  they  become  cleft  as  they  pass  through  it ;  at  the  distal 
end  they  may  terminate  in  tendon  bundles.  The  nerve-fibres  which 
pass  to  the  spindle  are  mostly  of  large  size  :  they  divide  after  reaching 
the  intrafusal  bundle,  but  retain  their  medullary  sheath  for  a  time, 
although  eventually  terminating  as  axis-cylinders  merely,  which  wind 
in  a  spiral  manner  around  the  intrafusal  muscle  fibres  (figs.  221,  222), 


180 


THE   ESSENTIALS   OF  HISTOLOGY. 


which  they  clasp  by  flattened  encircling  branches  {annulo-spiral  endings). 
Other,  much  finer,  medullated  fibres  also  pass  to  the  spindle  and  termi- 
nate in  neighbouring  parts  of  the  intrafusal  bundles  in  flower-like  or 
plate-like  expansions  (fig.  221).  According  to  some  observers  these  fine 
fibres  are  prolonged  from  the  annulo-spiral  endings  of  the  coarser  fibres ; 
but  Dogiel  states  that  they  may  run  independently  to  the  intrafusal 
bundle.  No  motor  nerve-fibres  appear  to  pass  into  the  spindles,  unless 
the  fine  fibres  above  mentioned  are  to  be  so  regarded,  nor  do  the 
muscle-fibres  of  the  spindle  undergo  atrophy  on  section  of  the  motor 
nerve-roots,  as  is  the  case  eventually  with  the  ordinary  muscle-fibres.  It 
is  not  uncommon  to  find  two  or  three  spindles  close  together  or  even 


B 


Fig.  224.— Nerve-ending  in  muscular  fibre  of  a  lizard  (Laceita  viridis). 

(Kiihne.) 
A,  end-plate  seen  edgeways  ;  B,  from  the  surface  ;  .«,  s,  sarcoleinma  ;  p,  p,  expansion  of 

axis-cylinder.     In  B  the  expansion  of  the  axis-cylinder  appears  as  a  clear  network 

branching  from  the  divisions  of  the  medullated  fibres. 

inclosed  in  a  common  sheath.  Muscle-spindles  are  few  in  number  in 
the  eye-muscles,  and  have  not  yet  been  found  in  the  muscles  of  the 
tongue,  but  otherwise  their  occurrence  is  general. 

In  the  frog  both  motor  and  sensory  nerves  may  teimiiiate  in  and  between 
the  same  muscle-tibres,  but  at  diflerent  parts  of  the  fibre.  It  is  not  known 
whether  the  muscle-tibres  of  the  spindles  also  receive  motor  nerves  in 
mammals. 

Another  kind  of  ending  of  sensory  fibres  in  muscle  has  been  described 

by  Ceccherelli,  in  the  form  of  an  arborisation  of  nerve-fibrils  around  the 
ends  of  the  muscle-fibres  which  are  inserted  into  tendon  (fig.  223). 

Ending  of  motor  nerves. — The  motor  nerves  to  muscles  terminate  in 
fine  ramifications  of  the  axis-cylinder  ;  in  striated  (voluntary)  muscles 
the  lamification  is  localised  in  special  organs  termed  motor  end-organs,  or, 
less  correctly,  end-plates. 


ENDING  OF  MOTOR  NERVES. 


181 


/y£^'tH« 


Fig.  225. — Motor  nerve-endings  in  the  abdominal  muscles  of  a  rat. 
Gold  preparation.     Magnified  170  diameters.     (Szymoiiowicz. ) 


Fig.  22G. — Motor  end-organ  of  a  lizard,  gold  preparation.     (Kiihne. ) 

n,  nerve-fibre  dividing  as  it  approaches  the  end-organ  ;  r,  ramification  of  axis-cylinder 
upon,  6,  granular  bed  or  sole  of  the  end-organ  m,  clear  substance  surrounding 
the  ramifications  of  the  axis-cylinder. 


182  THE   ESSENTIALS  OF  HISTOLOGY. 

In  voluntary  muscle,  the  nerves,  which  are  always  meduUated, 
terminate,  as  just  stated,  in  special  end-organs  (figs.  224  to  226).  A 
medullated  fibre  will  branch  two  or  three  times  before  ending,  and  then 
each  branch  passes  straight  to  a  muscular  fibre.  Having  reached  this, 
the  neurolemma  of  the  nerve-fibre  is  continued  into  the  sarcolemma  of 
the  muscle,  the  medullary  sheath  stops  short,  and  the  axis-cylinder  ends 
in  a  close  terminal  ramification  with  varicose  expansions  upon  its 
branches.  This  ramification  is  embedded  in  a  layer  of  granular 
nucleated  protoplasm  (sole)  (fig.  226,  b),  probably  a  development  of  the 
sarcoplasm  of  the  muscle.  In  some  cases  the  ramification  is  restricted 
to  a  small  portion  of  the  muscular  fibre,  and  forms  with  the  granular 
bed  a  slight  prominence  (eminence  of  Doyhre).     This  is  the  case  in  insects 


Fig.  227.— Ending  of  motor  nerves  in  rabbit's  muscle.     Reduced 

SILVER    METHOD.       (Cajal.) 

a,  axis-cyliiidur  of  entering  nerve  ;  h,  c,  d,  parts  of  terminal  ramification  showing 

network  of  neuro-fibrils., 

aud  mammals.  In  the  lizard  the  ramification  is  rather  more  extended 
than  in  mammals,  whilst  in  the  frog  it  is  spread  over  a  considerable 
length  of  the  fibre.  The  ramification  shows  a  fibrillar  structure 
(fig.  227),  which  is  especially  evident  at  the  enlargements.  In 
mammals  there  appears  to  be  only  one  end-plate  to  each  fibre,  while 
in  reptiles  there  may  be  several.      The  endplate  is  covered,  externally 


INVOLUNTARY   MUSCLE. 


1^3 


to  the   sarcolemnia,  by  an  expansion  of  the  sheath  of  Henle  of  the 
nerve-tibre  {fclohmnut). 

In  involuntary  muscle,  both  plain  and  cardiac  (fig.  228),  the  nerve- 
fibres,  which  near  their  termination  are  entirely  non-medullated,  end  in 
plexuses.  The  primary  plexuses  are  generally  furnished  with  ganglion- 
cells  in  abundance.     Such  gangliated  plexuses  are  best  developed  in 


Fig.  228. — Ending  of  nervefibkes  in  CARniAC  muscle.     (Smirnow.) 


connection  with  the  intestine.  From  the  cells  of  these  plexuses  other 
nerve-fibres  pass  which  form  secondary  plexuses  and  terminal  ramifica- 
tions amongst  the  contractile  fibre-cells,  to  the  surface  of  which  the 
endings  of  the  branches,  often  slightly  enlarged,  are  applied  (Huber 
and  de  Witt). 


184  THE   ESSENTIALS   OF  HISTOLOGY. 


LESSON   XX. 

STRUCTURE  OF   THE  LARGER  BLOOD-VESSELS. 

1.  Sections  of  a  medium-sized  peripheral  artery  and  vein,  e.g.  popliteal  or 
radial.  In  this  preparation  the  limits  of  the  vascular  coats  can  be  well  seen 
and  also  the  differences  which  they  present  in  the  arteries  and  veins  respec- 
tively. The  sections  may  be  stained  with  hiemalum  and  eosiu  or  with  orcein, 
and  mounted  in  dammar  or  xylol  balsam. 

2.  Mount  in  xylol  balsam  or  dammar  a  thin  slice  cut  from  the  inner 
surface  of  a  large  artery  which,  after  having  been  cut  open  longitudinally 
and  washed  with  distilled  water,  has  been  rinsed  with  nitrate  of  silver 
solution  and  then  with  distilled  water  and  exposed  to  the  sunlight.  The 
vessel  should  then  be  hardened  in  alcohol,  or  it  may  be  exposed  in  this  to  the 
light.  This  preparation  will  show  the  outlines  of  the  epithelium-cells  which 
line  the  vessel.     A  similar  preparation  may  be  made  from  a  large  vein. 

3.  A  piece  of  an  artery  which  has  been  macerated  for  some  days  in  33  per 
cent,  alcohol  is  to  be  teased  so  as  to  isolate  some  of  the  muscular  cells  of  the 
middle  coat  and  portions  of  the  elastic  layers  (networks  and  fenestrated 
membranes)  of  the  inner  and  middle  coats.  The  tissue  may  be  stained 
cautiously  with  diluted  htemalum,  and  glycerine  afterwards  added.  The 
muscular  cells  are  recognisable  by  their  irregular  outline  and  long  rod- 
shaped  nuclei.  Sketch  one  or  two  and  also  a  piece  of  the  elastic  network  or 
of  fenestrated  membrane.  The  fenestrated  membrane  is  best  obtained  from 
one  of  the  arteries  of  the  base  of  the  brain  ;  it  is  also  well  seen  in  the  arteries 
within  the  kidney. 

4.  Transverse  sections  of  aorta  and  carotid.  Notice  the  differences  in 
structure  between  these  and  the  section  of  the  smaller  artery. 

5.  Transverse  section  of  vena  cava  inferior.  Notice  the  comparatively 
thin  layer  of  circular  muscle,  and  outside  this  the  tliick  layer  of  longitudinal 
muscular  bundles  in  the  adv^entitia. 

Make  sketches  from  1,  4,  and  5  under  a  low  power,  from  2  and  3  under  a 
high  power. 


An  artery  is  usually  described  as  being  composed  of  three  coats,  an 
innei-  or  elastic,  a  middle  or  muscular,  and  an  external  or  areolar  (fig. 
229,  h,  c.'d).  It  is,  however,  more  correct  to  describe  the  wall  of  an 
artery  as  being  mainly  composed  of  muscular  and  elastic  tissue,  lined 
internally  by  a  pavement  epithelium  (endothelium),  and  strengthened 
externally  by  a  layer  of  connective  tissue  {adventitia). 

The  inner  coat  {tunica  intinvx)  is  lined  by  a  thin  layer  of  pavement 
epithelium  {endothelium),  the  cells  of  which  are  somewhat  elongated 
in  the  direction  of  the  axis  of  the  vessel  (fig.  230),  and  form  a 
smooth  lining  to  the  tube.     After  death  they  become  easily  detached. 


STRUCTURE   OF  ARTERIES. 


186 


The  endothelium  is  the  essential  layer  in  all  blood-vessels.  It  is  always 
the  first  part  to  be  developed,  and  in  some  it  remains  as  the  only  layer  of 
the  vessel.     This  is  the  case  with  all  true  capillaries  and  with  certain  veins, 


.^S^j^^^Sgr.:^ 


Fig.  229. — Transverse  section  of  part  op  the  wall  ok  the  posterior 
TIBIAL  ARTERY.     (75  diameters.) 

a,  epithelial  and  subepithelial  layers  of  inner  coat ;  6,  elastic  laj-er  (fenestrated  niom- 
braae)of  inner  coat,  appearing  as  a  brifjfht  line  in  section  ;  c,  muscular  layer  (middle 
coat);  d,  outer  coat,  consisting  of  connective  tissue  bundles.  In  the  interstices  of 
the  bundles  are  some  connective-tissue  nuclei,  and,  esisecially  near  the  muscular 
coat,  a  number  of  elastic  fibres  cut  across. 


and  also  with  the  lacunar  spaces  or  sinusoids,  which,  as  Minot  has  pointed 
out,  take  the  place  of  capillaries  in  certain  ])arts  (e.fj.  in  the  liver,  the 
medulla  of  the  suprarenal  capsules  and  the  Wolffian  body  of  the  embryo) ; 


Fig.  230. —Epithelial  layer  lining 

THE      posterior     TIBIAL      ARTERY. 

(250  diameters.) 


Fig.  231.— Portion  of  fenestrated 
membrane   of   henle   from    an 

ARTERY.      (Toldt. ) 


it  is  also  true  of  the  sinuses  of  erectile  tissue,  as  well  as  the  sihus-Iike 
blood-vessels  which  are  met  with  in  invertebrates.  In  some  structures  the 
endothelial  layer  of  the  blood-vessels  is  imperfect,  viz.  :  in  the  capillaries  and 


186 


THE   ESSENTIALS  OF  HISTOLOGy. 


blood-sinuses  of  the  spleen,  the  placental  mucous  membrane  of  the  pregnant 
uterus,  and  probably  the  sinusoids  (capillaries)  of  the  liver  :  in  these  places 


t 


Fig.  232. — Elastic  xetwokk  of  Fig.  233.— McscrLAK  fibre-cells  from 


ARTERT.      (Toldt.) 


SUPERIOR   thyroid   ARTERY.     (340  dia- 
meters.) 


Fig.  234. — Section  of  the  llngcal  artery.    (Griinstein.) 
■a,  epithelium  and  subepithelial  layer  of  inner  coat;   6,  its  elastic  layer;  c,  c,  d,  inner- 
most and  outermost  layers  of  middle  coat,  -with  elastic  fibres  passing  obliquely  to 
join  the  elastic  layers  which  bound  that  coat ;   (,  innermost  part  of  outer  coat  or 
adventitia,  showing  many  elastic  fibres  cut  across  ;  /.  outer  part  of  adventitia. 


STRUCTURE   OF   ARTERIES. 


187 


the  blood  finds  its  way  into  the  interstices  of  the  organ  and  conies  in  direct 
contact  with  the  tissue-cells. 

Next  to  the  endothelium  comes  an  elastic  layer  in  the  form  either  of 
elastic  networks  (fig.  232)  or  of  a,  fenestrated  membrane  (fig.  231).  In 
some  arteries  there  is  a  layer  of  fine  connective  tissue  intervening 
between  the  epithelium  and  the  fenestrated  membrane  {suhepithelial 
layer). 

The  middle  coat  (tunica  media)  consists  mainly  of  circularly  disposed 
plain  muscular  fibres,  but  it  is  also  pervaded  in  most  arteries  by  a 
network  of  elastic  fibres  which    are   connected  with  the   fenestrated 


4S?yfe:'^ 


'>-:^^^^^^  ^V"-^  ^'^ 


Fig.  235.— Section  of  thoracic  aorta  as  seen  under  a  low  power.     (Toldt.) 

a,  the  inner  coat  consisting  of  three  layers,  viz. :  1.  Epithelium  seen  as  a  fine  line. 
2.  Subepithelial  layer.  3.  Elastic  layers.  In  the  outer  part  of  the  inner  coat,  at  its 
junction  with  the  middle,  a  layer  of  longitudinal  muscular  fibres  is  represented  as 
cut  across.  6,  middle  coat  with  alternating  layers  of  muscle  and  elastic  mem- 
branes ;  c,  outer  coat  with  two  vasa  vasorum. 

membrane  of  the  inner  coat  and  are  sometimes  almost  as  much 
developed  as  the  muscular  tissue  itself.  This  is  especially  the  case 
with  the  larger  arteries,  such  as  the  aorta  and  the  carotid  and  its 
immediate  branches,  but  in  the  smaller  arteries  of  the  limbs  the 
middle  coat  is  composed  almost  purely  of  muscular  tissue.  The 
muscular  fibres  are  comparatively  short,  with  long  rod-shaped  nuclei, 
and  are  often  irregular  in  shape  (as  in  fig.  233),  especially  if  the 
middle  coat  contains  much  elastic  tissue. 

The  Older  coat  is  formed  of  connective  tissue  with  a  good  many 
elastic  fibres,  especially  next  to  the  middle  coat.  The  strength  of  an 
artery  depends  largely  upon  this  coat ;  it  is  far  less  easily  cut  or  torn 


188 


THE   ESSENTIALS   OF   HISTOLOGY. 


than  the  other  coats,  and  it  serves  to  resist  undue  expansion  of  the 
vessel.  Its  outer  limit  is  not  sharply  marked,  for  it  tends  to  blend 
with  the  surrounding  connective  tissue ;  hence  it  has  been  termed 
tunica  adventitia. 


intima< 


adventitia/   _ 


Fig.  236.— Section  of  aorta  more  magnified.     (Griinstein.) 

a,  epithelial  and  subepithelial  layers  of  inner  coat;  6,  c,  outer  layers  of  inner  coat 
containing  many  fine  elastic  fibres  ;  d,  e,  parts  of  outer  coat. 


STIUTCTUKE   OF   AUTERIES.  189 

Variations  in  structure. — The  aorta  (fis^-  235,  236)  differs  in  some  respects 
in  striuture  from  an  ordinary  artery.  Its  inner  coat  contaiuvS  a  consideral)le 
thickness  of  sube})ithelial  connective  tissue,  but  the  elastic  layers  of  this 
coat  are  chiefly  composed  of  fine  fibres,  ami  are  not  especially  marked  off 
from  those  of  the  middle  coat,  so  that  the  inner  and  middle  coats  appear 
blended  with  one  another.  On  the  other  hand,  there  is  a  very  great  develop- 
ment of  elastic  tissue  in  the  middle  coat,  forming  membranous  layers  which 
alternate  with  layers  of  the  muscular  tissue.  A  good  deal  of  connective 
tissue  also  takes  part  in  the  formation  of  the  middle  coat,  making  this  coat 
unusually  strong.  The  inner  and  middle  coats  constitute  almost  the  entire 
thickness  of  the  wall,  the  outer  coat  being  relatively  thin. 

The  other  variations  which  occur  in  the  arterial  system  have  reference 
chiefly  to  the  development  and  arrangement  of  the  muscular  tissue.  Thus  in 
many  of  tlie  larger  arteries  there  are  a  few  longitudinal  muscular  fibres  at 
the  inner  boundary  of  the  middle  coat,  and  in  .some  arteries  amongst  the 
circular  fibres  of  the  middle  coat.  This  is  the  case  in  the  aorta.  In  the 
part  of  the  umbilical  arteries  within  the  umbilical  cord  there  is  a  complete 
layer  of  longitudinal  fibres  internal  to  the  circular  fibi'es  and  another 
external  to  them,  wdiilst  the  amount  of  elastic  tissue  is  very  small.  Longi- 
tudinal fibres  are  also  present  in  some  other  arteries  (iliac,  superior 
mesentei'ic,  splenic,  renal,  etc.),  external  to  the  circular  fibres,  and  therefore 
in  the  outer  coat  of  the  artery. 


\'^,> 


V 


Fig.   237. — Transverse   section    of   part   of   the    wall    op   one   of   the 
POSTERIOR   TIBIAL   VEINS   (man).     About  200  diameters. 

a,  epithelial,  and  6,  subepithelial  layers  of  inner  coat ;  c,  middle  coat  consisting  of 
irregular  layers  of  muscular  tissue,  alternating  with  connective  tissue,  and  passing 
somewhat  gradually  into  the  outer  connective  tissue  and  elastic  coat,  d. 

The  veins  (fig.  237)  on  the  whole  resemble  the  arteries  in  structure, 
but  they  present  certain  differences.  In  the  internal  coat  the  same 
layers  may  be  present,  but  the  elastic  tissue  is  less  developed,  and 
may  be  quite  inconspicuous ;  it  seldom  takes  the  form  of  a  complete 
membrane.  The  epithelium  cells  are  less  elongated  than  those  of  the 
arteries.  The  middle  coat  {c)  contains  less  elastic  tissue  and  also  much 
less   muscular   tissue,    being    partly   occupied    by   bundles    of  white 


190 


THE   ESSENTIALS   OF  HISTOLOGY. 


connective-tissue  fibres.  These  are  continuous  with  those  of  the 
external  coat,  which  is  relatively  better  developed  in  the  veins  than 
in  the  arteries,  so  that,  although  thinner,  their  walls  are  often 
stronger. 

Many  of  the  veins  are  provided  with  valves,  which  are  crescentic 
folds  of  the   internal   coat   strengthened   by  a   little   fibrous   tissue : 

a  few  muscular  fibres  may  be 
found  in  the  valve  near  its  attach- 
ment. The  layer  of  the  inner 
coat  is  rather  thicker  and  the 
epithelium-cells  are  more  elon- 
gated on  the  side  which  is  subject 
to  friction  from  the  current  of 
blood  than  on  that  which  is  turned 
towards  the  wall  of  the  vessel. 

Variations  in  different  veins. — 

The  veins  vary  in  structure  more 
than  do  the  ai'teries.  In  many 
veins  longitudinal  muscular  fibres 
are  found  in  the  inner  part  of  the 
middle  coat,  as  in  the  iliac,  femoral, 
umbilical ;  the  umbilical  vein  witliiu 
the  umbilical  cord  having  three 
muscular  layers  like  the  correspond- 
ing arteries  ;  it  has  a  well-developed 
internal  elastic  layer.  In  other 
veins,  longitudinal  fibres  occur  ex- 
ternal to  the  cii'cularly  disposed 
fibres,  and  may  be  described  as 
belonging  to  the  outer  coat.  This 
is  the  case  with  the  abdominal  and 
especially  the  hepatic  portions  of 
the  inferior  vena  cava  (fig.  238),  and 
to  a  less  extent  with  the  hepatic  veins 
and  the  portal  vein  and  its  tribu- 
taries. In  the  superior  vena  cava,  in 
the  upper  part  of  the  inferior  vena 
cava  and  in  the  jugular,  subclavian 
and  innominate  veins  muscular  fibres 
are  almost  entirely  absent  in  the  middle  coat,  and  there  are  but  few  in  the 
adventitia.  The  veins  of  the  pia  mater,  brain  and  spinal  cord,  retina, 
and  bones,  and  the  venous  sinuses  of  the  dura  mater  and  placenta  have  no 
muscular  tissue. 

It  is  only  the  larger  veins,  especially  those  of  the  limbs,  that  possess 
valves.  They  are  wanting  in  most  of  the  veins  of  the  viscera  (although 
occurring  abundantly  in  some  of  the  tributaries  of  the  portal  vein),  in  those 
within  the  cranium  and  vertebral  canal,  in  the  veins  of  the  bones,  and  in 
the  umbilical  vein. 


Fig.  2:^.— Transverse  section  of  the 
inferior  vena  cava  of  the  dog. 
(Szymonowicz.)  Magnified  150  dia- 
meters. 

a,  intima ;  b,  thin  layer  of  circular  muscle  ; 
c,  thick  adventitia  with  longitudinal  muscu- 
lar bundles  ;  d,  a  vas  vasis. 


SMALLER    BLOOD-VESSELS.  191 


LESSOX    XXI. 

SMALLER  BLOOD-VESSELS  AND  LYMPH-VESSELS.  SEROUS 
MEMBRANES.  MICROSCOPIC  STUDY  OF  THE  CIRCULA- 
TION.    DEVELOPMENT  OF  BLOOD-VESSELS. 

1.  Take  a  piece  of  pia  mater  which  has  been  fixed  with  2  per  cent,  bichromate 
of  potassium  and  stained  with  hismatoxylin,  and  separate  from  it  some  of  the 
small  blood-vessels  of  which  it  is  chiefly  composed.  Mount  the  .shreds  in 
dilute  glycerine,  or  after  dehydrating  with  alcohol  and  passing  through  clove 
oil  they  can  be  mounted  in  dammar  or  xylol  balsam.  The  structure  of  the 
small  arteries  can  be  studied  in  this  preparation,  the  nuclei  of  the  epithelium 
and  of  the  muscular  coat  being  brought  distinctly  into  view  by  the  stain. 
The  veins  of  the  pia  mater  possess  no  muscular  tissue.  Capillary  vessels 
which  have  been  dragged  out  from  the  brain  in  removing  the  jjia  mater 
may  also  be  seen  in  this  preparation.  Sketch  two  small  arteries  of  different 
sizes,  giving  also  their  measurements. 

2.  Mount  in  dammar  or  xylol  balsam  a  piece  of  the  omentum  of  the 
rabbit,  stained  with  silver  nitrate.  The  membrane  should  be  stretched  over 
a  cork  or  a  ring  of  wood  or  vulcanite,  rinsed  with  distilled  water,  treated 
for  five  minutes  with  1  per  cent,  nitrate  of  silver  solution,  again  washed 
and  exposed  to  sunlight  in  spirit.  When  stained  brown,  the  preparation  is 
removed  from  the  light  and  placed  in  oil  of  cloves.  Pieces  may  now  be  cut 
off  from  the  membrane  and  mounted  in  balsam  or  dainraar  ;  they  should 
include  one  or  more  blood-vessels. 

This  preparation  is  intended  to  show  the  epithelium  of  the  smaller  blood- 
vessels and  accompanying  lymphatics,  and  also  the  epithelium  of  the  serous 
membrane.     Sketch  a  small  piece  showing  the  epithelium  of  the  vessels. 

3.  Mount  in  balsam  or  dammar  a  piece  of  the  central  tendon  of  the  rabbit's 
diaphragm  which  has  been  prepared  with  silver  nitrate,  the  pleural  surface 
liaving  been  first  brushed  to  remove  the  superficial  epithelium  and  thus 
enable  the  nitrate  of  silver  more  readily  to  penetrate  to  the  network  of 
underlying  lymphatic  vessels.  Observe  the  lymphatic  plexus  under  a  low 
power ;  sketch  a  portion  of  the  network.  If  the  peritoneal  surface  is 
focussed,  the  epithelium  which  covers  that  surface  will  be  seen,  and  oppo- 
site the  clefts  between  the  radially  disposed  tendon-bundles  stomata  may 
be  looked  for  in  this  epithelium. 

4.  Examine  sections  of  the  thoracic  duct.  These  may  be  made  in  the 
same  way  as  sections  of  the  blood-vessels. 

5.  Open  the  abdomen  of  a  freshly  killed  frog,  preferably  a  male,  and 
remove  the  abdominal  viscera,  taking  care  not  to  injure  the  membrane  or 
septum  at  the  back  of  the  abdomen,  which  lies  over  and  between  the  kidneys 
and  separates  the  peritoneal  cavity  from  the  cisterna  lympliatira  magna,  a 
large  lymph-space  in  which  the  aorta  and  vena  cava  are  contained.  Cut 
out  the  kidneys  along  with  as  much  as  possible  of  the  above  septum  ;  rinse 
with  distilled  water  ;  and  place  in  a  watch-glass  of  1  per  cent,  silver 
nitrate  for  5  minutes.  Rinse  again  in  distilled  water  and  expose  in  tap 
water  to  the  light.  When  slightly  browned  snip  oflF  a  portion  of  the  mem- 
branous septum,  float  it  flat  on  a  slide,  drain  ofl'  the  superfluous  water  and 


192 


THE   ESSENTIALS  OF   HISTOLOGY. 


allow  it  to  dry  ;  then  add  a  drop  of  xylol  balsam  or  daTumar  and  cover  the 
preparation. 

6.  Kill  a  frog  by  destroying  the  brain,  and  study  the  circulation  of  the 
blood  in  the  mesentery.  It  can  also  be  studied  in  the  web  of  the  frog's  foot, 
and  in  the  lung  and  tongue  of  the  frog  or  toad,  or  in  the  tail  of  the  tadpole 
or  of  any  small  fish.  But  for  observing  the  phenomena  attending  com- 
mencing inflammation  ami  the  emigration  of  leucocytes  from  the  vessels, 
the  mesentery  is  the  most  convenient  object.  The  frog  can  be  immobilised 
with  curari  or  by  placing  it  in  water  in  which  chloroform  or  ether  has  been 
shaken  up  :  a  lateral  incision  is  made  in  the  abdominal  wall,  a  loop  of 
intestine  drawn  out,  and  laid  over  a  ring  of  cork  which  is  fixed  to  a  glass 
plate  and  covered  with  a  thin  piece  of  glass.  The  membrane  must  be  kept 
wet  with  salt  solution. ^ 


The  coats  of  the  small  arteries  and  veins   are   much   simpler   in 
structure  than  those  of  the  larger  vessels,  but  they  contain  at  lirst  all 

(■     A    h  '-(J         a     b  B  h 


Fig.  239. — Small  artery,  A,  with  correspondixg  vein,  B,  treated  with 
ACETIC  ACin.     (Kolliker.)     (Magnified  350  diameters.) 

a,  external  coat  with  elongated  nuclei ;  h,  nuclei  of  the  transverse  muscular  tissue  of  the 
middle  coat  (when  seen  endwise,  as  at  the  sides  of  the  vessel,  their  outline  is 
circular) ;  e,  nuclei  of  the  epithelium-cells  ;  <.!,  elastic  laj'er  of  the  inner  coat. 


the  same  elements.  Thus  there  is  a  lining  endothelium  and  an  elastic 
layer,  the  two  together  forming  an  inner  a  at ;  a  middle  coat  of  circularly 
disposed  plain  muscular  tissue ;  and  a  thin  adventitia.  The  same 
differences  are  found  between  the  smaller  arteries  and  veins  as  with 
the  larger,  the  walls  of  the  veins  being  thinner  and  containing  far  less 
muscular    tissue    (fig.    239),    and    the    lining    epithelium-cells,    much 

^  For  details  of  the  methods  of  studying  the  circulation  and  also  of  injecting  the 
blood-vessels,  see  A  Course  of  Practical  Histology. 


SMALLER   BLOOD-VESSELS. 


193 


elongated  in  both  vessels,  are  far  longer  and  narrower  in  the  small 
arteries  than  in  the  corresponding  veins  (fig.   241). 

In  the  smallest  vessels  it  will  be  found  that  the  elastic  layer  has 
entirely  disappeared  in  the  veins,  and  the  muscular  tissue  is  consider- 
ably reduced  in  thickness  in  both  kinds  of  vessel.  Indeed,  it  is  soon 
represented  by  but  a  single  layer  of  contractile  cells,  and  even  these 
no  longer  form  a  complete  layer.  By  this  time  also,  the  outer  coat 
as  well  as  the  elastic  layer  of  the  inner  coat  have  disappeared  both 
from  arteries  and  veins.  The  vessels  are  reduced,  therefore,  to  the 
condition  of  a  tube  formed  of  pavement-epithelium  cells,  with  a  partial 
covering  of  circularly  disposed  muscular  cells. 


Fig.  240. 


-Transverse  section  of  a  small  artery  and  vein. 
Magnified  250  diameters. 


Even  in  the  smallest  vessels,  which  are  not  capillaries,  the  differences 
between  arteries  and  veins  are  still  manifested.  These  differences  may 
be  enumerated  as  follows  : — The  veins  are  larger  than  the  correspond- 
ing arteries ;  they  branch  at  less  acute  angles  ;  their  muscular  cells  are 
fewer,  and  their  epithelium-cells  less  elongated ;  the  elastic  layer  of 
the  inner  coat  is  always  less  marked,  and  sooner  disappears  as  the 
vessels  become  smaller. 

Capillary  vessels. — When  traced  to  their  smallest  branches  the 
arteries  and  veins  eventually  are  seen  to  be  continued  into  a  network 
of  the  smallest  blood-vessels  or  capillaries.  The  walls  of  these  are 
composed  only  of  flattened  epithelium-cells  (fig.  242)  continuous  with 
those  that  line  the  arteries  and  veins ;  these  cells  can  be  exhibited  by 
staining  a  tissue  with  nitrate  of  silver.  The  cell-outlines  are  not 
shown  in  developing  capillaries;  in  these,  silver  nitrate  stains  the  whole 

N 


194 


THE   ESSENTIALS   OF   HISTOLOGY. 


wall.  This  is  the  case  also  with  the  capillaries  of  the  villi,  those  of 
the  choroid  coat  of  the  eye  (Eberth),  and  those  of  the  kidney-glomeruli 
(Eanvier) :  in  all  these  places  the  walls  are  formed  of  a  syncytium. 


Fig.  241. — A  small  aetkky,  A,  and  vein,  V,  from  the  subcutaneous  con- 
nective   TISSUE    OF    THE    RAT,    TREATED    WITH    NITRATE   OP    SILVER,    WITH 

subsequent  STAINING  OF  NUCLEI.     175  diameters. 

«,  o,  epithelial  cells  with  b,  b  their  nuclei ;  m,  m,  transverse  markings  due  to  staining 
of  substance  between  the  muscular  fibre-cells  ;  c,  c,  nuclei  of  connective-tissue 
corpuscles  attached  to  exterior  of  vessel. 

The  capillaries  vary  somewhat  in  size  and  in  the  closeness  of  their 
meshes ;  their  arrangement  in  different  parts,  which  is  mainly  deter- 
mined by  the  disposition  of  the  tissue-elements,  may  best  be  studied 
in  injected  preparations,  and  will  be  described  when  the  structure 
of  the  several  organs  is  considered. 

In  the  transparent  parts  of  animals,  the  blood  may  be  seen  flowing 


c;apillary  vessels. 


I9r» 


through  the  cinuHary  network  from  the  arteries  into  the  veins.  The 
current  is  very  rapid  in  the  small  arteries,  somewhat  less  rapid  in  the 
veins,  and  slow  in  the  capillaries.  The  current  is  fastest  in  the  centre 
of  the  vessels,  slowest  near  the  wall  (inert  layer).  In  this  layer  the 
leucocytes  are  carried  along  by  the  stream  and  may  be  observed — 
especially  where  there  is  commencing  inflammation  of  the  part,  as  in 


Fig.  242. — Capillary  vessels  from 
the  bladder  of  the  cat,  mag- 
NIFIED. 

The  outlines  of  the  cells  are  stained  by 
nitrate  of  silver. 


Si:^*^^  t^^ 


Fig.    243.  —  Blood    plowing    through    a 

SMALL  VEIN  OF  THE  FROG's  MESENTERY. 
The  mesentery  had  been  exposed  for  a  short  time, 
so  that  there  was  commencing  inflammation 
and  many  of  the  white  corpuscles  are  observed 
sticking  to  and  even  passing  through  the  vas- 
cular wall,  a,  central  rapid  layer  containing 
the  coloured  corpuscles  ;  b,  outer  slower  layer 
(inert  layer)  containing  the  white  corpuscles. 


Fig.  244. — Ending  of  sensory  nerve-fibres  in  arborescences  in  the 

WALL   OF    A    SMALL   ARTERY.       (Dogiel. ) 

The  endotheliumcells  of  the  vessel  are  outlined  by  dotted  lines  and  the  outlines 
of  the  muscular  fibres  are  faintly  indicated. 


the  mesentery  in  consequence  of  exposure — to  adhere  to  the  inner 
surface  of  the  blood-vessels,  and  here  and  there  to  pass  through  the 
coats  of  the  small  vessels,  and  appear  as  migratory  cells  in  the  surround- 
ing connective  tissue  (fig.  243).  The  blood-platelets  are  also  to  be 
seen  in  the  inert  layer,  and  show  a  tendency  to  adhere  to  the 
wall  and  to  one  another  in  commencing  inflammation. 


196  THE   ESSENTIALS  OF   HISTOLOGY. 

Vessels  and  nerves  of  the  blood-vessels. — The  larger  arteries  and  veins 
possess  blood-vessels  {vdsa  vasorum)  and  lymphatics,  both  of  which  ramify 
chiefly  in  the  external  coat.  Nerves  are  distributed  to  the  raascular  tissue 
of  the  middle  coat,  after  forming  a  plexus  in  the  outer  coat.  Most  of  the 
nerves  ai'e  non-raeduUated.  But  there  are  a  certain  number  of  meduUated 
fibres  intermingled  with  the  non-niedullated  and  passing  to  end  in 
localised  arborescences  (fig.  244)  partly  in  the  adventitia,  partly  in  the 
intima.  These  nieduUated  fibres  are  doubtless  aff"erent ;  the  majority  of 
the  non-medullated  are  probably  efferent  (vaso-motors).  In  the  aorta  of 
man  and  in  some  of  the  larger  trunks  Pacinian  corpuscles  are  here  and 
there  met  with.  The  capillary  vessels  also  receive  nerve-fibres,  which  form 
a  fine  plexus  of  fibrils  in  close  contact  with  the  endotheliura-cells  of  which 
the  walls  of  these  vessels  are  composed.  Small  cells  are  found  at  intervals 
in  connection  with  tliese  plexuses,  but  whether  they  are  of  the  nature  of 
nerve-cells  or  not  is  uncertain. 

Development  of  the  blood-vessels. — The  blood-vessels  are  developed 
in  the  connective  tissue  or  in  the  mesenchyme  which  precedes  it,  the 
first  vessels  being  formed  in  the  vascular  area  which  surrounds  the 
early   embryo.      Their  development  may   be  studied  in   the  embryo 


Fig.  245. — Isolated  capillary  network  formed  by  the  junction  op 
a  hollowed-out  syncytium,  containing  coloured  blood-corpuscles 
in  a  clear  fluid. 

c,  a  hollow  cell  the  cavity  of  which  does  not  yet  communicate  with  the  network; 
J),  p,  pointed  cell  processes,  e-vtending  in  different  directions  for  union  with  neigh- 
bouring capillaries. 

chick  or  mammal,  in  the  omentum  of  the  new-born  rabbit,  or  in 
the  serous  membranes  and  subcutaneous  connective  tissue  of  foetal 
animals.  They  are  originally  developed  from  cells  (vaso-furmative  cells 
or  angiohlads)  which  become  hollowed  out  by  vacuolation  :  coloured 
blood-corpuscles  may  be  formed  within  them  (see  Development  of 
Blood-corpuscles,  Lesson  IL).  The  cells  branch  and  unite  with  one 
another  to  form  a  syncytium,  and  their  cavities  extend  into  the 
branches.  In  the  meantime  their  nuclei  multiply  and  become  dis- 
tributed along  the  branches,  cell-areas  being  at  a  later  stage 
marked  out  around  the  nuclei.  In  this  way  intercommunicat- 
ing   vessels — capillaries    containing    blood — are    produced    (fig.    245). 


DEVELOPMENT  OF   BLOOD-VESSELS. 


197 


These  presently  become  connected  with  previously  formed  vessels, 
which  extend  themselves  by  sending  out  sprouts,  at  first  solid,  and 
afterwards  hollowed  out.^  Even  the  larger  blood-vessels  appear  first 
to  be  developed  in  the  same  way  as  the  capillaries,  in  so  far  that  the 
epithelium  is  first  formed  and  the  muscular  and  other  tissues  are 
subsequently  added  ;  but  whether  they  are  formed  as  clefts  in  the 
mesoblastic  tissue,  which  become  bounded  by  flattened  cells,  or 
whether  as  a  hollowed-out  syncytium  has  not  been  definitely  ascer- 
tained. 


VCL 


Jnt        V  Ar 


Fig.  246. — Diagram  to  illustrate  the  development  of  blood-capillaries 
(right  side),  and  sinusoids  (left  side)  respectively.     (F.  T.  Lewis.) 

Int,  intestinal  entoderm  -with  outgrowth  ou  the  left  to  form  the  liver  and  gall-bladder, 
and  on  the  right  to  form  the  pancreas.  V.C.I. ,  vena  cava  inferior  ;  V.P.,  vena  portse; 
v.,  vein  and  Ar,  artery  supplying  pancreas.  It  is  seen  that  the  sinusoids  or  apparent 
capillaries  of  the  liver  are  formed  by  the  breaking  up  of  a  large  blood-space  into 
channels  by  the  growth  into  it  of  cell-columns  derived  from  the  hepatic  outgrowth  of 
the  entoderm. 


Sinusoids. — These  are  sinus-like  blood-spaces  between  the  cells  of  a 
tissue,  which  may  when  fully  developed  bear  a  superficial  resemblance 
to  blood-capillaries,  but  which  differ  essentially  from  them  both  in  their 
mode  of  development  and  in  their  relationship  to  the  connective  tissue, 
as  well  as  to  the  tissue-elements  of  the  organs  in  which  they  occur. 
Whereas  capillary  blood-vessels  are  developed  amongst  and  between 
the  tissue-elements  and  are  connected  with  and  grow  from  neighbouring 
capillaries  which  are  themselves  surrounded  by  areolar  tissue,  sinusoids 
make  their  first  appearance  in  the  form  of  comparatively  large  blood- 
spaces  connected  with  the  venous  (or  arterial)  system.  Into  these, 
the  walls  of  which  are  formed  only  of  a  single  layer  of  endothelial 
cells,  the  tissue-elements  of  the  developing  organ  (Wolffian  body, 
liver,  suprarenals,  blood-glands,  etc.)  grow,  invaginating  the  thin  wall 
and  forming  cell-trabeculse  within  the  sinus  (figs.  246,  247),  so   that 

^  Many  authorities  consider  that  new  blood-vessels  are  exclusively  formed  by 
sprouts  from  pre-existing  vessels,  and  regard  the  appearances  above  described 
as  being  due  to  retrogressive  development  of  an  already  formed  vascular  net- 
work (see  footnote,  p.  37). 


198 


THE   ESSENTIALS  OF   HISTOLOGY. 


the  cells  of  the  organ  are  directly  in  contact  with  the  invaginated 
endothelium,  and  are  only  separated  by  this  from  the  blood  contained 
within  the  sinus.  But  the  connection  may  become  yet  closer  than 
this,  for,  as  happens  in  the  liver,  the  invaginated  endothelium  may 


x300 

Fig.  247. — Liver  of  embkyo-chick  of  eleven  days.     (C.  S.  Minot.) 
/i.e.,  hepatic  cylinders;  Si,  sinusoids. 

become  defective,  so  that  the  blood  within  the  sinus  comes  into 
actual  contact  with  the  cells  of  the  organ,  and  runs  into  the 
interstices  between  them.  As  development  proceeds  these  interstices 
may  come  to  resemble  blood-capillaries  in  general  arrangement  and 
shape ;  but  the  resemblance  is  only  superficial,  and  the  intimate 
relationship  between  the  blood  and  the  tissue-elements,  which  are 
both  enclosed  within  the  original  sinus,  is  usually  maintained.  The 
distinctive  character  of  sinusoids  was  first  recognised  by  Minot. 


LYMPHATICS   OR   LYMPH-VESSELS. 

To  the  lymphatic  system  belong  not  only  the  lymphatic  vessels  and 
lymphatic  glands,  but  also  the  cavities  of  the  serous  membranes,  which  are 
moistened  with  lymph  and  are  in  open  communication  with  lymphatic 
vessels  Avhich  run  in  their  parietes. 

The  larger  Ijnnph-vessels  somewhat  resemble  the  veins  in  structure, 
except  that  their  coats  are  much  thinner  and  valves  much  more 
numerous.  In  lymphatics  of  smaller  size,  the  wall  of  the  vessel 
is  formed,  first,  by  a  lining  of  pavement-epithelium  cells  (lymphatic 
endothelium),  which  are  elongated  in  the  direction  of  the  axis  of  the 
vessel ;  and,  secondly,  by  a  layer  of  circularly  and  obliquely  disposed 
muscular  fibres.  In  the  smallest  vessels  (so-called  lymph-capillaries, 
which   are   generally  considerably  larger  than   the   blood-capillaries). 


LYMPH-VESSELS. 


199 


Fig.  248. — A  small  part  of  the  lymphatic  plexus  of  the  pleural  layer 

OP  the  diaphragm.     Magnified  110  diameters.     (Ranvier.) 
I,  lymphatics  with  cliaracteristic  epitheUuni  :  c,  cell-spaces  of  the  connective  tissue  here 
and  there  abutting  against  the  lymphatic. 


/ 


i. 


Fig.   249.— Nerves  of  a  lymphatic  vessel,   shown  by  methylene  blue, 

(Uogiel.) 

«,  a,  non-medullated  fibres  passing  to  the  vessel ;  h,  part  of  their  terminal  ramification. 


200 


THE   ESSENTIALS   OF  HISTOLOGY. 


there  is  nothing  but  the  epithelium  remaining,  and  the  cells  of  this 
are  frequently  not  more  elongated  in  one  direction  than  in  another, 
but  have  a  characteristic  wavy  outline  (fig.  248). 


Fig.  250.— Lymphatic  plexus  of  cextral  tendon  of  diaphragm  of  rabbit, 

PLEURAL  SIDE.      (Klein.) 

a,  larger  vessels  with  lauceolate  cells  and  numerous  valves  ;  6,  c,  lymph-capillaries 

with  wavy-bordered  cells. 

The  lymphatics  receive  numerous  nerve-fibres,  which  are  non- 
medullated,  and  which  end  in  a  ramification  of  the  finest  fibrils,  which 
are  distributed  to  the  coats  of  the  vessel  (fig.  249). 


LYMPH-VESSELS.  201 

Lymphatics  begin  either  in  the  form  of  plexuses,  as  in  serous  mem- 
branes (fig.  250),  or  of  lacunar  interstices,  as  in  some  of  the  viscera,  and 
all  transitions  occur  between  the  two. 

In  order  to  show  their  structure,  it  is  usual  to  stain  a  tissue 
vnth.  nitrate  of  silver ;  for  exhibiting  their  distribution  they  may  be 
injected  by  sticking  the  nozzle  of  an  injecting  cannula  into  any  tissue 
which  contains  them,  and  forcing  coloured  fluid  under  gentle  pressure 
into  the  interstices  of  the  tissue. 

In  silver  preparations  it  may  be  observed  that  the  lymphatics 
always  appear  in  the  form  of  clear  channels  in  the  stained  ground- 
substance  of  the  connective  tissue,  and  that  their  walls  are  in  close 
connection  with  the  cells  and  cell-spaces  of  that  tissue  (fig.  248).  But, 
except  in  the  case  of  the  serous  membranes,  no  open  communication  is 
observable  between  the  lymphatic  vessels  and  the  interstices  of  the 
connective  tissue,  although  from  the  readiness  with  which  they  can  be 
injected  from  the  latter  there  must  be  a  ready  means  of  passage  of  the 
interstitial  lymph  into  the  commencing  lymphatics.  The  lymphatic 
vessels  were  originally  described  by  Klein,  and  more  recently  by 
Retterer,  as  being  developed  from  hollowed-out  cells  in  the  same 
manner  as  the  blood-vessels,  and  by  Gulland  as  becoming  formed  at 
the  periphery  as  clefts  in  the  connective  tissue,  which  later  form  a 
connection  with  the  venous  system.  But  the  investigations  of  Eanvier, 
recently  confirmed  by  Lewis  and  others,  tend  to  show  that  the 
lymphatic  trunks  grow  out  from  the  venous  system,  and  gradually 
penetrate  into  the  peripheral  parts  of  the  embryo. 

Serous  Membranes. 

The  serous  membranes,  which  may  be  conveniently  studied  in 
connection  with  the  lymphatic  system,  are  delicate  membranes  of 
connective  tissue  which  surround  and  line  the  internal  cavities  of  the 
body,  and  are  reflected  over  many  of  the  thoracic  and  abdominal  viscera; 
in  passing  to  which  they  form  folds  (such  as  the  mesentery),  within 
which  blood-vessels,  lymphatics,  and  nerves  are  conducted  to  the  viscera. 

The  inner  surface  is  lined  by  a  continuous  layer  of  'pavement- 
epithelium  {endothelium)  (fig.  251),  which  is  very  distinct  in  nitrate 
of  silver  preparations.  In  some  places  there  are  apertures  in  the 
epithelium  which  lead  directly  into  subjacent  lymphatic  vessels. 
These  apertures  are  called  stomata,  and  are  sometimes  surrounded  by 
special  cells  (fig.  251,  J?).  They  are  numerous  upon  the  peritoneal 
surface  of  the  diaphragm,  but  are  present  in  most  serous  membranes. 
They  are  nowhere  better  studied  or  more  easily  seen  than  in  the 
peritoneal   membrane   at   the    back  of   the   abdominal   cavity   in   the 


^02  THE   ESSENTIALS   OF   HISTOLOGY. 

frog.  This  membrane  lies  between  and  at  the  sides  of  the  kidneys, 
and  serves  to  separate  the  peritoneal  cavity  from  the  large  lymph- 
space  just  behind  it.  If  the  membrane  is  prepared  by  the  nitrate  of 
silver  method  the  stomata  and  the  cells  which  surround  them  on  either 
side  of  the  membrane  are  well  shown. 

The   pavement-epithelium    of  the   serous   membrane   rests   upon  a 
homogeneous   basement-membrane,    which   is  especially   well   marked 


[\  1- 


-sh- 


y^ 


IE:-: 


V 


Fig.  251. 

1.  Epithelium  from  the  posterior  part  of  the  prog's  peritoneum,  showing 

THREE      stomata      LEADING      INTO     THE     CISTERNA      LYMPHATICA     MAGNA. 

(v.  Ebner,  after  Schweigger  Seidel  and  Dogiel.) 

2.  A  PORTION  OF  EPITHELIUM  FROM  THE  PERITONEAL  SURFACE  OF  THE  RABBIT's 

DIAPHRAGM.       THREK  PORES  ARE  VISIBLE  BETWEEN  THE  EPITHELIUM  CELLS. 

(v.  Ebner,  after  Ludwig  and  Schweigger  Seidel.) 

in  the  serous  membranes  of  man.  The  rest  of  the  thickness  of  the 
membrane  is  composed  of  connective  tissue,  with  a  network  of  fine 
elastic  fibres  near  the  inner  surface. 

The  cavities  of  the  serous  membranes  are  originally  formed  in  the 
embryo  as  a  cleft  in  the  mesoderm  (pleuro-peritoneal  split,  coelom) 
which  becomes  lined  with  epithelium,  outside  which  the  coelomic  wall 
eventually  becomes  differentiated  into  the  serous  membrane. 


LYMPH-GLANDS.  203 


LESSON    XXIT. 
LYMPH-GLANDS.     TONSILS.     THYMUS. 

1.  Sections  of  a  lymph -inland  which  has  been  hardened  either  in  formol 
or  potassium  bichromate,  or  in  chromic  acid  or  picric  acid  followed  by 
alcohol,  stained  in  bulk,  and  embedded  in  paraffin.  Or  the  sections  may  be 
stained  with  luematoxylin  and  eosin.  Notice  (1)  the  fibrous  and  muscular 
capsule,  with  trabecular  extending  inwards  from  it  through  the  cortex  and 
anastomosing  with  one  another  in  the  medulla,  (2)  the  dense  lymphoid 
tissue  (adenoid  tissue  of  some  authors)  forming  large  masses  in  the  cortex 
(cortical  uoilules)  and  rounded  cords  in  the  medulla  (medullary  cords). 
Notice  also  the  clearer  channel  or  lymph-sinus  which  everywhere  intervenes 
between  the  fibrous  tissue  and  the  lymphoid  tissue.  Observe  the  fine  fibres 
and  branched  cells  which  bridge  across  this  channel. 

Make  a  general  sketch  under  a  low  power  of  a  portion  of  the  cortex 
together  with  the  adjoining  part  of  the  medulla,  and  under  a  high  power 
drawings  of  small  portions  of  cortex  and  medulla. 

The  retiform  tissue  of  the  lymph-glands  has  already  been  studied  (p.  75). 

2.  Sections  of  a  In^mal  lymph-gland.  These  may  be  readily  found  in  the 
neck  of  the  ox,  in  the  neighbourhood  of  the  large  blood-vessels.  Stain  with 
eosin  and  htematoxylin  or  with  eosin  and  methylene  blue.  Notice  that  the 
channels  around  the  lymphoid  nodules  (or  some  of  them)  contain  blood 
instead  of  lymph. 

3.  In  sections  of  tonsil  prepared  similarly  to  those  of  the  lymphatic 
gland,  notice  the  large  amount  of  lymphoid  tissue,  partly  collected  into 
nodules.  Observe  also  that  the  stratified  epithelium,  which  covers  the 
mucous  membrane  here  as  elsewhere  in  the  mouth,  is  infiltrated  with  lymph- 
corpuscles.  The  tonsil  is  beset  with  pit-like  recesses,  with  mucus-secreting 
glands  opening  into  the  pits. 

4.  Lymphoid  nodules  of  mucous  membranes.  In  other  mucous  membranes 
besides  that  of  the  back  of  the  mouth  and  pharynx,  collections  of  lymphoid 
tissue  occur  which  resemble  those  of  the  tonsils  ;  such  nodules  form  the 
solitary  glands  of  the  stomach  and  intestines  and  the  agminated  glands  of 
the  small  intestine,  and  are  also  found  in  the  trachea  and  bronchial  tubes  and 
in  the  oesophagus.     They  may  be  studied  later  in  sections  of  those  parts. 

5.  Sections  of  the  thymus  gland  of  an  infant  or  young  animal.  Notice 
that  the  masses  of  lymphoid  (?)  tissue  which  form  the  lobules  of  the  gland  are 
separated  by  septa  of  connective  tissue,  and  that  the  lobules  show  a  distinc- 
tion into  two  parts,  cortical  and  medullary.  There  are  no  lymph-paths. 
Observe  the  differences  of  structure  of  the  cortex  and  medulla,  and  especially 
notice  the  concentric  corpuscles  in  the  medullary  part. 

Make  a  sketch  of  one  of  the  lobules  under  a  low  power  and  of  a  small 
part  of  the  medulla  under  a  high  power,  including  one  or  two  concentric 
corpuscles.     Measure  the  latter. 


Lymph-Glands. 


Structure  of  a  lymph-gland. —A  lymph-gland  (lymphatic  gland)  is 
composed  of  a  framework  of  fibrous  and  plain  muscular  tissue,  which 


204 


THE   ESSENTIALS   OF   HISTOLOGY. 


incloses  and  supports  the  proper  glandular  substance,  but  is  everywhere 
separated  from  it  by  a  narrow  channel,  bridged  across  by  cells  and  fibres, 
which  is  known  as  the  lymph-channel.  The  frameu-ork  consists  of  an 
envelope  or  capsule  (fig.  252,  c),  and  of  trabeculce  (tr),  which  pass  at 
intervals  inwards  from  the  capsule,  and  after  traversing  the  cortex  of 
the  gland,  divide  and  reunite  with  one  another  to  form  a  network  of 
fibrous  bands.  At  one  part  of  the  gland  there  is  usually  a  depression 
{hilus),  and  at  the  bottom  of  this  the  medulla  comes  to  the  surface 
and  its  fibrous  bands  are  directly  continuous  with  the  capsule. 


Fig.  252. — Diagrammatic  section  of  lymph-glaxd.    (Sharpey.) 

a.l.  afiferent,  e.l.  efferent  lymphatics  ;  C,  cortical  substance  ;  M,  reticulating  cords  of 
medullary  substance;  l.h.  lymphoid  tissue;  l.s.  lymph-sinus;  c,  capsule  sending 
trabecute,  tr,  into  the  substance  of  the  gland. 

The  proper  glandular  substance  {l.h.)  is  composed  of  lymphoid  tissue, 
i.e.  a  fine  reticulum  with  the  meshes  thickly  occupied  by  lymph- 
coi-puscles.  It  occupies  all  the  interstices  of  the  gland,  forming  com- 
paratively large  rounded  masses  in  the  cortex  (lymjihoid  nodules,  C), 
which  may  be  two  or  three  deep,  and  smaller  reticulating  cord-like 
masses  (lymphoid  cords,  M)  in  the  medulla. 

The  cells  which  bridge  across  the  lymph-channel  in  the  medulla 
(fig.  254,  c)  are  branching  nucleated  cells  which  often  contain  pigment, 
so  that  this  part  of  the  gland  has  a  dark  colour.  Some  may  contain 
disintegrating  erythrocytes.  The  lymph-channel  is  bridged  across  not 
only  by  these  branched  cells,  but  also  by  fibres   derived    from   the 


LYMPH-GLANDS. 


205 


capsule  and  trabeculse,  which  pass  to  the  lymphoid  tissue  and  become 
lost  in  its  reticulum.  But  the  fibres  are  often  completely  concealed  by 
the  cells. 

Afferent  lymph-vessels  (fig.  252,  a.l.)  enter  the  lymph-channels  after 
ramifying  in  the  capsule,  and  the  lymph  is  conveyed  slowly  along 
the  channels  of  the  cortical  and  medullary  part  towards  the  hilus, 
taking  up  many  Ij'mph-corpuscles  in  its  passage.  At  the  hilus  it 
is  gathered  up  by  an  efferent  vessel  or  vessels  (e.l.)  taking  origin  in 
the  lymph-sinuses  of  the  medulla. 


Fig.  253. — Sectio.v  of  .\  ltmph-gl.\nd  from  the  neck  of  an  eight  year 
OLD  CHILD,     (v.  Ebner.)     x  13. 

c,  capsule;  c.n,  cortical  nodules,  some  witts  germ-centres;  l.c,  lymphoid  cords  of 
medulla  (dark);  l.p,  lymph-path  (light);  s,  cortical  sinus;  t,  trabeculae;  r,  vein; 
I,  eflferent  lymph-vessels,  accompanying  and  partly  surrounding  blood-vessels,  6^ 


The  efferent  lymphatics  always  contain  many  more  lymph-corpuscles 
than  those  which  enter  the  gland,  for  lymph-corpuscles  are  constantly 
being  formed  by  mitotic  division  of  the  pre-existing  cells  in  the 
glandular  substance,  especially  in  the  clearer  centre  of  each  cortical 
nodule  {germ-centre  of  Flemming) ;  they  gradually  find  their  way 
into  the  lymph-channel. 

The  leucocytes  of  the  germ-centres  frequently  show  in  sections  peculiar 
darkly-coloured  bodies — the  staiaable-bodies  of  Flemming — the  origin  of 
which  has  not  been  determined. 


206 


THE   ESSENTIALS  OF   HISTOLOGY. 


An  artery  passes  into  each  gland  at  the  hilus  ;  its  bi-anches  are 
conveyed  at  first  along  the  fibrous  cords,  but  soon  become  surrounded 
by  the  lymphoid  cords,  where  they  break  up  into  capillaries  (fig.  254,  d). 
The  blood  is  returned  by  small  veins,  which  are  conducted  along  the 
fibrous  trabecula3  to  the  hilus. 


Fig.  254. — Section  of  the  medullary  substance  of  a  lymph-gland. 

300  diameters.     (Recklinghausen.) 

a,  a,  a,  lymphoid  cords  ;  c,  lyniph-sinu.s ;  b,  b,  trabeculas ;  d,  d,  capillary  blood-vessels. 

In  some  lymph-glands  the  fibrous  trabeculse  are  very  slightly  de- 
veloped, so  that  the  gland  seems  in  section  to  be  almost  uniformly  a 
mass  of  lymphoid  tissue,  pervaded  by  lymph-channels  and  with  clearer 
rounded  nodules  (germ-centres)  scattered  about,  especially  in  the  cortex 
(fig.  253).  This  is  the  case  with  most  of  the  lymph-glands  of  man  and 
some  other  animals.  In  other  animals,  such  as  the  dog  and  ox,  the 
trabecule  are  very  well  developed  and  contain  much  muscular  tissue. 

Nerve-fibres   pass  to  lymph-glands   and   appear   to   be   distributed 

chiefly  as  non-medullated  fibres  to  the  plain  muscular  tissue  of  the 

blood-vessels  and  trabeculse. 

Ordinary  lymph-glands  are  confined  to  mammals,  biit  Vincent  and  Harrison 
have  found  hsemal  lymph-glands  in  birds. 

Haemal  lymph-glands. — In  many  animals  a  certain  number  of  lymph- 
glands  are  observable  which   have  a  red  colour.     Some  of  these  on 


H^MAL  LYMPH-GLANDS.  207 

section  show  that  what  corresfjonds  to  the  peripheral  lymph-channel 
in  ordinary  lymph-glands  is  in  them  occupied  by  blood.  Others 
have  the  greater  part  of  the  interior  occupied  by  large  sinuses  filled 
with  blood  ;  but  some  parts  have  the  ordinary  structure  of  a  lymph- 
gland.  The  names  hcemal  glands  and  hcemal  lymph-glands  (Robertson) 
have  been  given  to  these  organs.  The  blood  passes  into  the  sinuses 
from  the  arterial  capillaries,  which  probably,  as  in  the  spleen,  become 
incomplete,  and  open  into  the  tissue  interstices,  from  which  at  other 


Fig.  255. — Section  through  one  of  the  crypts  of  the  tonsil.     (Stohr.) 

«,  e,  stratified  epithelium  of  surface  of  mucous  membrane,  continued  into  cr3'pt ;  ./;  /, 
follicles  or  nodules  of  the  lymphoid  tissue,  which  is  elsewhere  diffuse  ;  some  show 
clear  "  germ -centres "  ;  opposite  each  nodule  numbers  of  lymph-cells  are  passing 
through  the  epithelium  ;  s,  masses  of  cells  which  have  thus  escaped  from  the  organ 
to  mix  with  the  saliva  as  salivary  corpuscles. 

parts  the  small  veins  in  like  manner  arise.  Like  the  spleen  these 
haemal  glands  show  cells  (phagocytes)  which  contain  red  blood- 
corpuscles  in  various  stages  of  transformation  into  pigment. 

Some  haemal  glands  are  said  by  Weidenreich  to  have  no   lymph- 
channels,  but  this  statement  requires  confirmation. 

The  Tonsils. 
The  tonsils  are  two  masses  of  lymphoid  tissue  placed  one  on  each 
side  of  the  pharynx,  into  which  they  project.     They  are  covered  on 
the  free  surface  with  the  stratified  epithelium  of  the  mucous  membrane. 


208 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fig.  256.— Lymphatics  of  a  peyee'.s  patch,  injected  with  silver  nitrate; 
CAT.     (Kolliker.)    Magnified  8.5  diameters. 

/,  a  lymphoid  nodule  or  follicle  \  j' ,  its  base,  resting  upon  the  muscular  coat,  m  ;  i.m., 
submucosa ;  I,  lymph-vessels  ;  «,  sinus-like  enlargement  of  lymph-vessel  surrounding 
follicle. 


Fig.  257.  —Developing  lymphoid  nodcles  from  the  gcineapig's  omentum. 

(Klein.) 

A    perilymphatic  nodule  ;   a,  lymphatic ;   c,  its  endothelium  ;   e,  lymph-coniuscles  ;    6, 

'  accumulation  of  lymphoid  tissue  on  one  side  of  it ;  d,  blood-capillanes  withm  this. 
B   endolymphatic  nodule  consisting  of  an  enlarged  lymphatic  vessel,  d,  within  which 
'    is  a  capillary  network  c,  c,  an  artery,  h,  and  a  vein,  a ;  «,  lymphoid  tissue  within 
the  lymphatic,  its  branched  cells  being  joined  to  and  derived  from  the  lymphatic 
endothelium/. 


THE   TONSILS.  209 

and  this  surface  is  pitted  with  apertures  which  lead  into  recesses  or 
crypts  in  the  substance  of  the  organ  (fig.  255).  These  recesses  are  all 
lined  by  a  prolongation  of  the  stratified  epithelium,  and  into  them 
the  ducts  of  numerous  small  mucous  glands  open.  The  tonsils  are 
composed  almost  entirely  of  lymphoid  tissue,  which,  besides  being 
diffused  over  the  whole  organ,  is  at  intervals  aggregated  into 
nodules,  in  which  the  lymph-cells  are  more  closely  arranged  than 
elsewhere.  In  the  clear  centre  (germ-centre)  of  some  of  these  nodules 
active  multiplication  of  the  lymph-cells  by  mitosis  is  constantly 
proceeding,  and  is,  in  fact,  the  cause  of  the  formation  of  nodules 
in  the  tissue,  as  in  other  organs  in  which  lymphoid  tissue  occurs. 
Even  the  epithelium  which  covers  the  tonsils  is  infiltrated  with 
lymph-corpuscles  (Stohr),  and  these  mav  also  wander  out  on  to  the 
free  surface,  and  become  mingled  with  the  saliva  as  salivary  corpuscles. 

The  lymphoid  tissue  is  highly  vascular,  and  contains  many  lymphatics. 

The  mucous  membrane  of  the  neighbouring  part  of  the  pharynx 
and  of  the  back  of  the  tongue  and  that  of  the  upper  part  of  the 
pharynx  near  the  orifices  of  the  Eustachian  tubes  shows  crypts 
and  masses  of  lymphoid  tissue  similar  in  structure  to  those  of  the 
tonsils. 

Other  Ly3iphoid  Structures. 

Lymphoid  tissue  occurs  in  many  other  parts  of  the  body  in 
addition  to  the  lymphatic  glands  and  tonsils,  although  it  may  not, 
as  in  these  structures,  constitute  the  bulk  of  the  organ.  Thus  it 
is  found  in  many  mucous  membranes,  such  as  those  of  the  intestine 
and  of  the  respiratory  tract,  both  in  a  diffuse  form  and  also  collected 
into  nodular  masses  which  are  like  the  cortical  nodules  of  a  lymphatic 
gland,  and  may,  like  these,  be  partially  surrounded  by  a  lymph-sinus. 
In  the  intestine  such  nodules  constitute  the  so-called  solitary  glands  and 
Peyefs  patches.  The  lymphatics  form  plexuses  of  large  sinus-like 
vessels  which  to  a  large  extent  enclose  the  nodules  (fig.  256).  In 
the  spleen  a  large  amount  of  lymphoid  tissue  is  found  etisheathing 
the  smaller  arteries,  and  also  expanded  into  nodular  masses  [Malpighian 
corpuscles  of  the  spleen).  All  these  structures  will  be  studied  subse- 
quently. Lymphoid  tissue  also  occurs  in  considerable  amount  in 
the  serous  membranes,  especially  in  young  animals ;  in  the  adult  it 
is  here  mostly  replaced  by  adipose  tissue. 

Development  of  lymphoid  tissue. — Lvmph-glauds  are  developed  in 
connection  with  plexuses  of  lyiuph-vessels,  an  accumulation  of  retiform 
tissue  and  lymph-cells  taking  place  either  external  to  and  around  the 
lymphatics  {perilymphatic  formation) ;  or  some  of  the  lymphatics  are  dilated 

0 


210  THE   ESSENTIALS   OF   HISTOLOGY. 

into  a  sinus  or  sinuses  and  the  formation  of  lymphoid  tissue  occurs  within 
it  {endoli/mph/jtic  formation)  (fitf.  257,  a  and  b).  When  there  is  a  develop- 
ment of  lymphoid  tissue  outside  the  lymphatic  vessels  this  may  form  a 
considerable  accumulation  before  the  foin)ation  of  lymph -paths  within  the 
tissue.  Blood-vessels  are  early  developed  amongst  the  lymphatic  plexuses, 
and  by  these,  according  to  GuUand,  the  first  lymph-corpuscles  of  the 
lymphoid  tissue  are  brought  to  the  gland. 

Tlie  marginal  sinus  is  produced  by  the  fusion  of  a  number  of  lymph- 
vessels  which  surround  the  accumulation  of  lymphoid  tissue,  while  in  the 
situation  of  the  future  hilus  other  lymph-vessels  grow  into  the  glandular 
substance  and  form  channels  which  subdivide  it  up  into  cords  and  nodules 
(Kling).  The  branched  cells  of  the  lymph-path  are  said  to  be  derived  from 
the  lymphatic  endothelium. 

The  axillary  glamls  were  found  by  Stiles  to  increase  in  number  and  size 
during  lactation,  diminishing  again  after  lactation  has  ceased.  In  the 
developing  tonsils  GuUand  occasionally  found  nests  of  epithelial  cells 
detached  from  the  surface  epithelium,  .somewhat  like  tho.se  found  per- 
manently in  the  thymus. 

Thymus. 
The  thymus  gland  is  an  organ  which  in  man  is  found  only  in 
the  embryo  and  during  infancy.  It  is  composed  of  a  number 
of  lobules  (fig.  258)  varying  in  .size,  which  are  separated  from  one 
another  by  septa  of  connective  tissue,  along  which  the  blood-vessels 
and  lymphatics  pass  to  and  from  the  lobules.  Each  lobule  shows 
// 

''^'       '  '      ^^W 

'-'-^^ — c 


\. 


V  H         ■  % 


\ 


''<^^>?*. 


Fig.  2.58. — A  lobcle  of  the  thymus  ok  a  child,  as  seen  under  a  low  poweb 
c,  cortex  ;  c,  conceutric  corpuscles  within  medulla  ;  6,  blood-vessels  ;  tr,  trabeculae. 

plainly,  when  examined  with  a  low  power,  a  distinction  into  an  outer 
cortical  and  an  inner  medullary  portion.  The  cortical  part  of  the 
lobule  is  imperfectly  divided  into  nodules  by  trabeculae  of  connective 
tissue.  It  is  highly  vascular,  and  is  superficially  similar  in  structure 
to  the  lymphoid  tissue  of  the  lymph-glands  and  tonsils,  with  which 
it  also   agrees   in    exhibiting   numerous   indications    of  indirect    cell- 


THYMUS. 


211 


division,  l)ut  without  definite  germ-centres.  Besides  leucocytes  it 
contains  a  number  of  peculiar  granular  cells.  The  medulla  is  more 
open  in  its  texture,  and  its  reticulum  is  formed  by  large  transparent, 
branched  cells  (fig.  259),  which  are  sometimes  massed  together  and 
then  resemble  epithelium-cells.  The  medulla  contains  fewer  lymph- 
corpuscles  than  the  cortex  and  has  a  clearer  aspect.  Connective  tissue 
fibres  are  not  wholly  absent  from  it.     Within  the  medulla,  but  not 


i.m'W  ' 


fiG.  259. — Section  of  medulla  of  thv.mcs,  showing  br.^nched  (epithelial) 

CELLS   OF   RETICCLUM   AND  A  CERTAIN  NUMBER  OF  LYMPHOID  CELLS  IN  THE 

MESHES.     (Hammar.) 


in  the  cortex,  are  found  peculiar  concentrically  striated  bodies  (the 
concentric  corpuscles  of  Hassal,  figs.  258,  260),  which  are  "  nests "  of 
flattened  epithelial  cells  arranged  concentrically  around  one  or  more 
central  cells,  which  have  often  undergone  a  degenerative  process. 
Sometimes  these  corpuscles  are  compound,  two  or  three  being  grouped 
together  and  similarly  enclosed  by  flattened  cells.  They  represent 
part  of  the  remains  of  an  epithelial  tube,  which  forms  the  thymus 
rudiment  of  the  early  embryo  and  is  derived  from  certain  of  the 
branchial  clefts.  According  to  the  observations  of  Hammar  the 
reticulum  of  the  gland  is  also  derived  from  this  epithelium,  and 
Stohr  believes  that  the  apparent  lymphoid  cells  of  the  gland  have 
a  similar  origin.  The  inference  drawn  by  J.  Beard  from  his  observ- 
ations  in   Elasmobranchs    that   the   thymus    is   the    original    seat    of 


212 


THE   ESSENTIALS   OF   HISTOLOGY. 


formation  of  leucocytes  in  the  embryo,  appears  from  more  extended 
investigations  to  be  incorrect. 

Nucleated  red  blood- corpuscles  (erythroblasts),  similar  to  those  found 
in  red  marrow,  have  also  been  described  in  the  thymus  (J.  Schaffer), 
and  occasionally  cysts  lined  by  ciliated  epithelium  are  found.  In 
some  animals  islands  of  striated  muscular  cells  are  seen  in  the 
medulla.     Multinucleated  giant-cells  are  also  found  (Watney). 

,^  The    lobules,    the    cortex    especially,   are 

abundantly  supplied  with  capillary  blood- 
vessels. In  man  the  arteries  penetrate  to 
the  junction  of  cortex  and  medulla,  and 
give  off  most  of  their  capillaries  radially 
into  the  cortical  nodules.  Veins  pass  away 
both  from  the  surface  of  the  lobules  and 
to  a  less  extent  directly  from  the  medulla. 
The  mode  of  distribution  of  the  lymphatics 
has  not  been  definitely  ascertained,  but  none 
are  seen  within  the  lobules.  Nevertheless, 
large  lymphatic  vessels,  containing  many 
lymphocytes,  issue  from  the  interstitial 
connective  tissue  of  the  thymus,  but  in  what  way  they  are  connected 
with  the  lobules  has  not  been  ascertained. 

In  the  human  subject  the  thymus  gland  undergoes  after  childhood 
a  process  of  retrogression,  its  lobules  ceasing  to  grow  and  becoming 
surrounded  and  concealed  by  a  c|uantity  of  adipose  tissue  which 
develops  in  the  interstitial  connective  tissue  of  the  gland.  Eventually 
the  lobules  atrophy. 


Fia.  200. — Elements  of  the 
THYMUS.  300  diameters. 
(Cadiat.) 

a,   lymph-corpuscles ;    b,   cou- 
centric  corpuscle. 


STRUCTURE   OF  THE   SPLEEN.  213 


LESSON    XXIII. 

STRUCTURE  OF  THE  SPLEEN,  SUPRARENAL  CAPSULES, 
THYROID  BODY,  AND  PITUITARY  BODY. 

1.  Sections  of  the  spleen  hardened  in  Mliller's  fluid  or  formol  and  stained 
with  hjeniatoxylin  and  eosin.  Notice  the  trabeculse  extending  into  the 
substance  of  the  oroan  from  the  capsule.  Notice  also  that  the  glandular 
substance  is  of  two  kinds,  (1)  lymphoid  tissue  accumulated  around  the  small 
arteries  and  here  and  there  massed  to  form  h/mphoid  nodules — the 
Malpighian  corpuscles — and  (2)  a  tissue — the  red  pulp — consisting  of  a 
reticulum  of  fibrils  and  branching  cells  :  this  tissue  contains  blood  in  its 
interstices. 

Sketch  part  of  a  section  under  a  low  power  and  a  small  portion  of  the  pulp 
under  a  high  power. 

2.  Sections  across  a  suprarenal  capsule  hardened  in  2  per  cent,  bichromate 
of  potassium.  In  sections  not  otherwise  stained,  notice  the  deep  brown 
coloration  of  the  medulla  (action  of  the  chromic  salt).  Stain  other  sections 
with  eosin  and  hematoxylin.  Examine  first  with  a  low  power,  noticing 
the  general  arrangement  and  extent  of  the  cortical  and  medullary  parts  of 
the  orgari,  and  making  a  general  sketch  which  shall  include  both.  After- 
wards sketch  carefully  under  the  high  power  a  group  of  cells  from  each 
part  of  the  organ. 

3.  Sections  of  the  thyroid  body  stained  with  eosin  and  lipematoxylin. 
Notice  the  vesicles  lined  with  cubical  epithelium  and  filled  wnth  a  "colloid" 
substance  which  becomes  stained  with  hsematoxylin.  Sketch  one  or  two 
vesicles.  Measure  several  vesicles.  The  sections  will  probably  also  include 
one  or  more  parathyroids. 

4.  Sections  (antero-posterior)  through  the  pituitary  body.  Notice  the 
(epithelial)  anterior  lobe  separated  by  a  cleft  from  the  (nervous)  posterior 
lobe.  (The  anterior  part  of  the  posterior  lobe  is  also  covered  by  an 
epithelial  layer.) 

5.  Injected  preparations  of  these  organs  may  also  be  studied  :  the  spleen 
is  usually  naturally  injected  with  blood. 


The  Spleen. 

The  spleen  is  the  largest  of  the  so-called  ductless  glands.  It  appears 
to  be  functionally  connected  with  the  blood,  white  blood-corpuscles 
being  formed  and  coloured  blood-corpuscles  being  submitted  to  destruc- 
tion within  it. 

Like  the  lymph-glands,  the  spleen  is  invested  with  a  tibrous  and 
muscular  aipsule  (fig.  261),  which  is  however  stronger  and  has  far 
more  plain  muscular  tissue ;  outside  the  capsule  is  a  covering  derived 
from  the  serous  membrane.     The  capsule  sends  bands  of  trabecule 


Sl4  THE   ESSENTIALS   OF   HISTOLOGY. 

into  the  organ,  and  these  join  with  a  network  of  similar  trabeculae 
which  pass  into  the  gland  at  the  hilus  along  with  the  blood-vessels. 
In  the  interstices  of  the  framework  thus  constituted  lies  a  soft  pulpy 
substance  containing  a  large  amount  of  blood,  and  therefore  of  a  deep 
red  colour,  dotted  within  which  are  here  and  there  to  be  seen  small 
round  bodies,  whiter  than  the  pulp  in  the  fresh  organ  but  darker  in 


Fig.  261. — Vertic.vl  section  of  a  portion  of  the  monkey's  spleen,  as 
seen  with  a  low  power. 

stained  sections,  the  Mulpighian  corpuscles  of  the  spleen.  These  are 
composed  of  lymphoid  tissue  which  is  gathered  up  into  masses  which 
envelop  the  smaller  arteries,  whilst  the  red  pulp  which  everywhere 
surrounds  them  and  which  forms  the  bulk  of  the  organ  is  composed 
(Carlier)  of  a  close  network  of  connective  tissue  fibrils  (fig.  262), 
partly  covered  by  flattened  and  branched  cells  (fig.  263).  Passing  into 
the  pulp  and  communicating  with  its  interstices  are  capillary  blood- 
vessels which  are  connected  with  the  terminations  of  the  arteries ; 
whilst  in  other  parts  venous  channels — characterised  in  the  human 
spleen  by  an  encirclement  of  reticulum-fibres,  possibly  of  an  ela.stic 
nature  (fig.  264),  and  by  the  presence  of  a  layer  of  highly  characteristic, 


STRUCTURE   OF   THE   SPLEEN. 


215 


Fig.  262. — Reticulum  of  spleen,  golgi  method.     (Oppel.) 
a,  Malpighian  coi-p>iscle  ;  b,  part  of  its  reticulum  :  c,  condensed  reticulum  at  its  margin  ; 
d,  more  open  tissue  next  to  this  ;   e,  wall  of  arteriole ;  /,  capillaries  of  Malpighian 
corpuscle  ;  g,  reticulum  of  arteriole  expanding  into  that  of  the  Malpighian  corpuscle. 


Fig.  203. — Small  veins  of  spleen  pulp  with  reticular  tissue.     (Hoyer. ) 

The  veins,  which  are  invested  by  encircling  fibres,  show  gaps  in  their  walls  whereby 

they  communicate  with  the  interstices  of  the  pulp. 


216 


THE   ESSENTIALS   OF   HISTOLOGY. 


comparatively  thick  and  prominent  endothelium-cells,  ■which  exhibit 
a  longitudinally  striated  structure — course  through  the  pulp  and  bring 
the  blood  which  has  passed  into  its  interstices  from  the  arterial 
capillaries  towards  the  larger  veins  of  the  organ,  which  run  in  the 
trabeculse,  and  are  by  them  conducted  to  the  hilus.  The  arteries, 
which  are  also  at  first  conducted  from  the  hilus  along  the  trabeculae 
into  the  interior  of  the  organ,  presently  leave  the  trabeculse,  and  their 


Fig.  264. — Venous  spaces  of  spleen  pulp,  showing  the  encircling  fibres 

IN  THEIR  walls.     Man.     (v.  Ebner.) 

cv,  capillary  veins  ;  p,  pulp  (the  tissue  elements  are  not  represented). 


external  coat  becomes  gradually  converted  into  a  thick  sheath  of 
lymphoid  tissue  which  invests  them  in  the  remainder  of  their  course, 
and  in  places  becomes  swollen  into  the  Malpighian  corpuscles  already 
mentioned.  The  small  arteries  distribute  a  few  capillaries  to  the 
Malpighian  corpuscles,  and  then  break  up  into  pencils  of  capillary 
vessels  which  open  into  the  interstices  of  the  pulp.^ 

The  Malpighian  corpuscles  frequently  but  not  always  show  a 
clearer  central  nodule  or  gerin-centre,  characterised  b)^  the  presence  of 
numerous  mitoses ;  and  the  stainable  bodies  of  Flemming  (see  p.  205) 
are  also  seen  in  them. 

^It  is  right  to  state  that  many  authorities  hold  that  the  arterial  capillaries 
open  into  the  venous  sinuses  and  that  the  blood-sj'stem  of  the  spleen  is  there- 
fore a  closed  one,  the  blood-corpuscles  passing  into  the  pulp-interstices  by 
diapedesis. 


STRUCTURE   OF  THE   SPLEEN. 


217 


fl»  ^.^1? 


9 


Fig.  265.— Thin   section   of   spleen-pulp    of   child,    highly   magnified, 

SHOWING     the    apparent    MODE     OF     ORIGIN     OF     A    SMALL     VEIN     IN    THE 

INTERSTICES  OF  THE  PULP.     Magnified  400  diameters. 
a,  blood  in  pulp  ;  a',  blood  in  vein  ;  6,  phagocyte  in  vein  ;  c,  branched  cell  of  pulp  ;  d,  splenic  cell. 


Fig.  266. — A  giant  cell  from  the 
SPLEEN  OF  A  KITTEN.  Magnified 
400  diameters. 


Fig.  267. — A  vertical  section 
of  the  suprarenal  body 
of  a  fcetus,  twice  the 
natural  size,  showing 
the    distinction    between 

THE     medullary    AND     COR- 
TICAL        SUBSTANCE.  (A. 

Thomson.) 

V,  issuing  vein ;  r,  summit  of  kidney. 


218  THE   ESSENTIALS   OF   HISTOLOGY. 

The  special  cellular  elements  of  the  spleen-pulp  are  of  three  kinds,  viz. 
(1)  peculiar,  large,  amoeboid  2>hagocytic  cells,  (2)  megakaryocytes  or  giant 
cells,  and  (3)  branched  and  generally  flattened  cells  which  assist  in  forming 
the  spongeworlc.  The  pulp  also  contains  all  the  corpuscular  elements 
of  blood.  The  phagocytic  cells  are  frequently  found  to  contain  coloured 
blood-corpuscles  in  their  interior  in  various  stages  of  transformation 
into  pigment.  They  occur  both  in  the  interstices  of  the  pulp  and  in 
the  venous  sinuses  and  veins,  where  they  are  often  filled  with  erythro- 
cytes (fig.  265).  The  giant  cells  are  most  frequent  in  young  animals 
(fig.  266)  :  their  function  has  not  been  ascertained.  The  branched 
cells  of  the  spongeworlc  are  probably  of  the  same  nature  as  the 
endothelium  cells  of  the  terminal  capillaries  and  veins  of  the  pulp. 
They  are  connected  with  one  another  and  with  the  endothelial  cells 
of  the  small  vessels  by  branches.  The  phagocytic  spleen  cells  are 
perhaps  derived  from  them. 

Nucleated  coloured  corpuscles  are  found  in  the  embryo,  and 
occasionally  after  birth,  in  the  spleen-pulp.  The  blood  of  the 
splenic  vein  is  very  rich  in  leucocytes. 

The  lymphatics  of  the  spleen  run  partly  in  the  trabeculse  and  capsule, 
and  partly  in  the  lymphoid  tissue  ensheathing  the  arteries.  They  join 
to  form  larger  vessels  which  emerge  together  at  the  hilus.  There  are 
no  lymphatics  in  the  spleen  pulp. 

The  nerves,  which  are  numerous  and  mostly  non-medullated,  are 
distributed  to  the  muscular  tissue  of  the  arteries  and  to  that  in  the 
capsule  and  trabeculre. 

Mall  states  that  tlie  distribution  of  the  trabeculcB  and  of  the  blood-vessels 
within  the  spleen  is  such  as  to  indicate  a  differentiation  of  the  pulp  into 
divisions  which  he  tenns  "spleen  lobules,"  each  of  which  has  its  own 
arteriole  and  venule,  and  in  which'  tlie  pulp  is  arranged  in  columns  or 
cords  surrounded  by  venous  spaces.  It  must,  however,  be  understood  that 
there  is  nothing  of  the  nature  of  partitions  separating  such  lobules  :  to  all 
appearance  the  pulp  is  in  continuity  throughout  the  organ. 


The  Suprarenal  Capsules. 

The  suprarenal  capsules  (adrenals)  belong  to  the  class  of  bodies 
known  as  ductless  glands,  but  they  are  entirely  different  in  structure 
and  function  from  the  spleen  and  lymphatic  glands.  A  section  through 
the  fresh  organ  (fig.  267)  shows  a  cortex  which  is  striated  verti- 
cally to  the  surface,  and  of  a  yellowish  colour,  and  a  medidla  which  is 
soft  and  highly  vascular,  and  of  a  dark-red  colour.  The  whole  organ  is 
invested  by  a  fibrous  capsule  which  sends  fibrous  septa  inwards  through 
the  cortical  substance  (fig.  268,  a),  subdividing  this  for  the  most  part 


THE   SUPKAKKNAL  CAPSULES. 


219 


into  columnar  groups  of  cells  {.:onaf((scicvhif(i,  r).  Immediately  under- 
neath the  capsule,  however,  the  groups  are  more  rounded,  and  the  cells 
tend  to  assume  a  columnar  form  (zotui  glomerulosa,  b),  whilst  next  to 
the  medulla  they  have  a  reticular  arrangement  (:on(i  rHimlarU,  d). 


hf  ( 


ivi 


Fig.  268. — Vertical  .section  of  cortex  of  suprarenal  of  dog.    (Bohm 

and  V.   Davidoff).     Magnified  about  1.50  diameters. 

[a,  capsule  ;  b,  zona  glomerulosa  ;  c,  zona  fasciculata  ;  d,  zona  reticularis. 

The  cells  which  form  the  cortical  substance  are,  for  the  most  part, 
polyhedral  in  form  ;  each  contains  a  clear  round  nucleus,  and  there 
are  often  yellowish  oil-globules  in  their  protoplasm.  No  arteries  and 
veins  penetrate  between  these  cell.<=!,  both  these  and  the  lymphatics  of 
the  cortex  running  in  the  fibrous  septa  between  the  columns  of  cells, 
which  they  surround  with  a  capillary  network.  In  the  zona  reticularis 
the  capillaries  widen  out  and  occupy  the  spaces  between  the  cell-- 
columns  (fig.  268,  d).  The  lymphatics  communicate  with  fine  canals 
between  the  cells  of  the  cortex. 


220 


THE   ESSENTIALS  OF  HISTOLOGY. 


The  cells  of  the  medulla  (fig.  2G9)  are  more  irregularly  disposed. 
They  are  supported  by  a  network  of  elastic  fibres.  They  lie  in  very 
close   relation    to   the   large  capillary  blood-spaces   (sinusoids)   \vhich 


f^j^ 


.■du 


'}  €> 


fs,^ 


0  @ 


<£} 


& 


<iiS, 


''rf.'^'iS] 


Fig.  269. — Section  showing  zona  reticularis  of  cortex,  r,  and  medulla, 
m,  of  suprarenal  of  dog.     (Sz^ymouowicz. )    Magnified  384  diameters. 


pervade  the  medulla  and  they  probably  pour  a  secretion  directly  into 
the  blood.  Their  protoplasm  is  granular ;  in  some  animals  it  contains 
a  brownish  pigment,  but  in  man  the  dark  red  colour  of  the  medulla  is 
due  to  the  blood  contained  in  the  large  sinusoid  spaces  b}^  which 
it  is  pervaded,  and  which  receive  the  blood  after  it  has  traversed 
the  capillaries  of  the  cortex.  A  few  arterioles  pass  straight  to  the 
medulla  through  the  cortex.     One  large  vein  usually  passes  out  at 


THE   Ti[YR011)    BODY.  221 

the  hilus  in  the  anterior  surface  of  the  gland.  Investing  the  larger 
veins  are  longitudinal  bundles  of  plain  muscular  fibres ;  but  most  of 
the  veins  have  only  an  endothelium.  Numerous  nerves,  after  traversing 
the  cortical  substance,  are  distributed  throughout  the  medulla,  where 
they  form  a  close  plexus  provided  here  and  there  with  ganglion-cells. 
The  cells  of  the  medulla  are  characterised  by  staining  brown  by 
chromic  acid  and  its  salts,  provided  the  organ  is  fresh  (chromophil 
or  chromaffin  cells). 

The  medulla  of  the  suprarenal  capsule  is  developed  from  cells  which 
become  detached  from  the  rudiments  of  the  sympathetic  ganglia,  and 
are  therefore  of  ectodermal  origin.  The  cortex  is  developed  from 
mesoderm. 

The  Thyroid  Body. 
The   thyroid   body  consists   of  a  framework   of  connective   tissue 
inclosing  numerous  spherical  or  oval  vesicles  (fig.  270)  which  are  lined 


'■«'::re! 


i^^  ■%<^^...j^''^m:       i)ffi:i 


i^^^±>3^^^JL*%'*J*Jsi^:.s.&^:^Js'.i 


Fig.  270. — Srction   of   human   thyroid.      (Szymonowicz. )     Magnified  about 

180  diameters, 
a"  vesicle  occupied  by  colloid,  which  has  partly  shrunk  away  from   the  epithelium  ; 

6,  epithelium  of  a  large  vesicle  ;  c,  c,  epithelium  of  vesicles  which  are  cut  tangen- 

tially  ;  d,  interstitial  connective  tissue. 

with  cubical  epithelium-cells ;  these  often  contain  granules  of  a  fatty 
character.  The  cavities  of  the  vesicles  are  usually  occupied  by  a 
peculiar  viscid  liquid  (colloid)  which  is  coagulated  by  alcohol  and 
which  then  becomes  stained  with  hsematoxylin.     A  similar  material 


222 


THE   ESSENTIALS   OF   HISTOLOGY. 


has  been  found  in  the  lymphatics  of  the  gland,  and  may  often  be 
detected  also  in  the  interstices  of  the  connective  tissue. 

The  bloodvessels  of  the  thyroid  are  numerous  and  give  a  deep 
red  colour  to  the  organ.  The  capillaries  form  close  plexuses  round 
the  vesicles  (fig.  271),  and  even  extend  between  the  lining  epithelium 
cells. 

Parathyroids. — In  close  proximity  to  or  embedded  in  the  substance 
of  the  thyroid  are  always  to  be  found    four   small   glandular  organs 


:iir*^v 


Fig.  271. — Thyroid  of  dog 
injected. 


Fig.  272.— P.akathyroid  of  monkey. 
(Vincent  and  Jolly.) 

'I,  paratJiyroid  tissue;  h,  blood-vessels;  c, 
connective  tissue ;  d,  junction  of  para- 
thyroid with  thyroid ;  c,  thyi-oid  vesicles ; 
«',  colloid. 


of  different  structure  from  the  thyroid  proper,  although  somewhat 
resembling  its  embryonic  condition  (fig.  272).  These  bodies,  one  of 
which  usually  lies  on  the  lateral  and  one  on  the  mesial  surface  of  each 
lateral  lobe,  are  formed  of  columns  of  granular  epithelium-cells,  with 
a  very  vascular  connective  tissue  between  the  columns.  If  left  after 
removal  of  the  thyroid,  they  are  stated  to  undergo  hypertrophy,  and 
to  develop  a  vesicular  structure  (Vincent  and  Jolly).  Besides  these 
bodies,  there  is  also  frequently  to  be  found  in  connexion  with  the 
thyroid  a  small  mass  of  lymphoid  tissue  which  resembles  the  thymus 
tissue  in  structure,  and,  like  it,  contains  concentric  corpuscles. 


CAROTID   AND   COCCYGEAL   GLANDS. 


These  are  minute  glandtilar  orgaiis  without  ducts,  lying  respectively 
at  the  bifurcation  of  the  carotid  artery  and  in  front  of  the  apex  of  the 
coccyx.  They  are  composed  of  polyhedral  cells,  with  numerous  blood- 
capillaries  between  them.     In  the  carotid  gland  the  cells  are  collected 


CAROTID   AND   COCCYGEAL  GLANDS. 

ft 


223 


Fig.   273. — A   clump   or   cell-ball   from   the   carotid  gland,  injected. 

(Schaper.) 
a,  arteriole ;    r,    venules ;   c,    sinus-like    capillary   within    nodule ;   gl,   group  of  gland 

cells ;  c,  boundary  of  nodule  surrounded  by  lymph  space  ;  d,  inter-nodular  connective 

tissue  of  gland. 


Fig.  274. — Section  of  coccygeal  gland.     (Walker.) 
1,  blood-spaces;  2,  epithelium;  3,  connective  tissue. 


224 


THE   ESSENTIALS   OF  HISTOLOGY. 


into  spheroidal  clumps,  in  the  coccygeal  gland  into  irregular  nodules. 
The  blood-vessels,  at  least  in  the  coccygeal  gland,  have  a  sinusoidal 
character  (Walker).  Amongst  the  cells  are  some  which  stain  dark 
brown  with  chromic  acid  like  those  of  the  medulla  of  the  suprarenal 
capsules  (chromophil  cells).  A  certain  number  of  such  cells  occur 
also,  according  to  Kohn,  in  sympathetic  ganglia. 


The  Piti'itaey  Body. 

The  pituitary  body  or  gland  (hypophysis  cerebri)  is  a  small  reddish 
mass  which  lies  in  the  sella  turcica,  and  is  connected  with  the  third 
ventricle  by  the  infundibulum.  It  consists  of  two  lobes,  a  larger 
anterior   and    a   smaller    posterior   (fig.    275).      The   anterior    lobe    is 


Jhrs  post ![^^.'^.,','^.-%.j; 

Pars  one '-r - -^Yj^- 


Cranium  "" 

Fig.  275.— Section  thbough  hypophysis.     (Ediuger.) 


■4 

,1    ■   -  -    n^' 

Fig.  27.5a.— Skctios  of  akteriob  lobe  of  hypophysis  of  ox.    (Dostoievsky.) 

W,  blood-sinuses  ;  c,  cell-strands  containii  g  clear  cells  ;  d,  strands  of  darker  granular 
cells.     Other  strands  contain  both  kinds  of  cell.  ' 


THK   PITUITARY   BODY.  '      225 

originally  developed  as  a  hollow  protrusion  of  the  buccal  epithelium. 
It  consists  of  a  number  of  tubules,  which  are  lined  by  epithelium 
and  united  by  connective-  tissue.  In  some  of  the  tubes  the 
epithelium  is  ciliated,  and  occasionally  a  colloid  substance  is  found 
in  them,  but  for  the  most  part  the  lumen  of  the  tubules  has  become 
obliterated  in  the  adult,  and  they  present  the  appearance  of  solid 
cell-masses  between  which  are  numerous  large  venous  capillaries, 
perhaps  sinusoids.  Some  of  the  cells  arc  clear,  others  darkly  granular 
in  appearance  (fig.  275  a). 

The  'posterior  lobe  of  the  pituitary  body,  which  is  developed  from  the 
infundibulum  of  the  third  ventricle,  consists  chiefly  of  vascular  connec- 
tive tissue  and  neuroglia,  but  it  also  includes  masses  of  cells  of  an 
epithelial  character  {pars  intermedia),  which  are  continuous  with  those 
of  the  anterior  lobe.  It  is  partly  separated  from  the  'anterior  lobe  by 
a  cleft-like  space  containing  glairy  fluid.  In  man  the  posterior  lobe  is 
stated  to  contain  no  cells  in  the  adult  of  distinctly  nervous  character, 
but  it  receives  many  nerve-fibres  which  arise  from  large  cells  in  the 
grey  matter  just  behind  the  optic  chiasma,  some  of  which  penetrate 
into  the  glandular  substance. 


226       •  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSONS  XXIV.  AND  XXV. 
THE  SKIN. 

1.  Sections  of  skin  from  the  palmar  surface  of  the  fingers.  The  skin  is 
hardened  in  picric  acid  or  formol,  followed  by  alcohol.  The  sections  are 
made  vertical  to  the  surface,  and  should  extend  down  as  far  as  the  sub- 
cutaneous tissue.  Notice  the  layers  of  the  epidermis  and  their  different 
behaviour  to  staining  fluids.  Notice  also  the  papilloe  projecting  from  the 
corium  into  the  epidermis  and  look  for  tactile  corpuscles  within  them.  In 
very  thin  jjarts  of  the  sections  the  fine  intercellular  channels  in  the  deeper 
parts  of  the  epithelium  (see  Lesson  VII.)  may  be  seen  with  a  high  power.  The 
convoluted  tubes  of  the  sweat-glands  are  visible  here  and  there  in  the  deeper 
parts  of  the  corium,  and  in  thick  sections  the  corkscrew-like  channels  by 
which  the  sweat  is  conducted  through  the  ejjidermis  may  also  be  observed. 
Make  a  sketch  showing  the  general  structure  under  a  low  power,  and  other 
sketches  to  exhibit  the  most  important  details  under  a  high  power.  Measure 
the  thickness  of  the  epidermis  and  the  length  of  the  papillse. 

2.  Sections  of  the  skin  of  the  scalji,  vertical  to  the  surface  and  parallel 
to  the  slope  of  the  hair-follicles,  and  others  parallel  to  the  surface,  and 
therefore  across  the  hair-follicles.  Stain  and  mount  in  the  same  way  as  in 
the  last  preparation.     Examine  also  the  structure  of  the  hairs. 

In  these  preparations  the  details  of  structure  of  the  hairs  and  hair-follicles, 
together  with  the  sebaceous  glands  and  the  little  muscles  of  the  hair-follicles, 
are  to  be  made  out. 

3.  Vertical  sections  of  the  nail  and  nail-bed.  To  cut  such  hard  structures 
as  the  nail  it  is  best,  after  fixing  with  picric  acid  or  formol  followed  by  75 
p.c.  alcohol,  to  soak  the  tissue  in  strong  gum  arable  for  a  few  days,  then  place 
it  in  an  appropriate  position  upon  a  cork  or  upon  the  object-carrier  of  a 
microtome,  and  plunge  the  whole  into  70  per  cent,  alcohol.  This  renders  the 
gum  hard,  and  enables  sections  to  be  cut  of  sufficient  fineness.  A  plane  iron 
should  be  used  with  the  microtome,  since  the  hardness  of  the  nail  will  turn 
the  edge  of  a  razor.  To  remove  the  gum  the  sections  are  placed  in  water  for 
a  few  hours  ;  they  may  then  be  stained  and  mounted.  Notice  the  ridges 
(not  papillae)  of  the  corium,  projecting  into  the  epidermis.  Observe  also  the 
distinction  of  the  epidermis  into  Malpighian  layer  and  nail  proper. 

4.  Mount  a  section  from  a  portion  of  skin  in  which  the  blood-vessels  have 
been  injected,  and  notice  the  distribution  of  the  capillaries  to  the  sweat- 
glands,  to  the  hair-follicles,  and  to  the  papillary  surface  of  the  corium. 

5.  The  cells  which  compose  the  nails  and  hairs  can  be  isolated  by  warming 
a  small  piece' of  nail  or  hair  in  strong  sidplmric  acid  ;  after  this  treatment 
they  are  readily  separated  from  one  another  by  piessure  upon  the  cover- 
glass. 

6.  Sections  of  mammary  gland  during  lactation.  The  gland  may  be  fixed 
in  Zenker's  fluid  (see  Appendix)  and  the  sections  stained  with  ha^matoxylin 
and  eosin. 

The  skin  is  composed  of  two  parts,  epidermis  and  cutis  vera  (fig.  276). 

The  epidermis,  or  scarf  skin,  is  a  stratified  epithelium  (fig.  277).     It 

is  composed  of  a  number  of  layers  of  cells,  the  deeper  of  which  are 


THE   SKIN. 


22  ^ 


soft  and  protoplasmic,  and  form  the  reie  mucosurii  of  Malpighi,  whilst 
the  superficial  layers  are  hard  and  horny,  this  horny  portion  sometimes 


^t^^- 


) 

i 

>) 

It 
\ 


>-^,-^ 


stratum 
corneuin 


.  rete  mucosum 


-cutis  vera 


fS^^ 

- 

• ',% 

^ 

^  ^d 

L-^,'  •  " 

'M- : 

%^\ 

■•:  ^/ 

\>-\  -.   - 

-  "   "S* 

-'vj/     . 

K-: . 

sweat  glands 


adipose  tissue 


Fig.  276.— Vertical  section  thkodgh  the  skin  of  the  sole  of  the  foot. 

Magnified  about  2-5  diameters. 

constituting  the  greater  part  of  the  thickness  of  the  epidermis.  The 
deepest  cells  of  the  rete  mueosum,  which  are  set  on  the  surface  of  the 
cutis  vera,  are  columnar  in  shape.     In  the  coloured  races  of  mankind 


228 


THE   ESSENTIALS   OF   HISTOLOGY. 


these  cells  contain  pigment-granules.  In  the  layers  immediately  above 
them  the  cells  are  polyhedral.  Between  all  these  cells  of  the  rete 
mucosum  there  are  fine  intercellular  clefts  which  separate  the  cells 
from  one  another,  but  are  bridged  across  by  fibres  which  pass  from 
cell  to  cell,  and  also  through  the  substance  of  the  cells  (Ranvier, 
Delepine).     The  intercellular  channels  serve  for  the  passage  of  lymph, 


!<r*'.-^<:>^-«f:- 


stratum 
corneum 

stratum  lucidum 

stratum 

icranulosum 


^  ^    P^-'^ 


rete  mucosum 


-*^i  -cutis  vera 


Fig.   277.— Vertical  sectiox  through  the  .skix  of  the  p.\lmar  side  of 
the  finger,  showing  two  pafill.e  (oxe  of  which  coxtaixs  a  tactile 

CORPUSCLE)     AXn     THE     DEEPER     LATER    OF     THE     EPIDERMIS.        Magnified 

about  200  diameters. 

and  within  them  occasionally  lymph-corpuscles  may  be  found,  often 
haA^ng  a  stellate  figure  from  becoming  shaped  to  the  interstices. 

The  superficial  layer  of  the  rete  mucosum  is  formed  of  somewhat 
flattened  cells  filled  with  granules  or  droplets  of  a  material  (eleidin) 
which  stains  deeply  with  carmine  and  haematoxylin  (stratum  granulosum, 
fig.  277;  fig.  278).  This  is  not  sharply  marked  off"  from  the 
cells  of  the  rete  mucosum  which  lie  next  to  it,  for  many  of  these 
show  similar   granules,   although    they   less    completely  fill   the   cell. 


THE   SKIN.  229 

Superficial  to  the  stratum  granulosum  is  a  layer  in  which  the  cell- 
outlines  are  indistinct  and  the  cells  contain  flakes  or  larger  droplets  of 
a  hyaline  material  (kerato-hyalin),  which  stain  less  intensely  than  the 
granules  in  the  last  layer,  and  which  tend  to  run  together.  This 
layer  has  a  clear  appearance  in  section,  and  is  known  as  the  stratum 
lucidum.  Immediately  superficial  to  the  stratum  lucidum  is  the  horny 
part  {stratum  corneum)  of  the  epidermis.  It  is  composed  of  a  number 
of  layers  of  epithelium  cells,  the  nuclei  of  which  are  no  longer  visible. 
These   cells   near   the    surface   take   the   form   of    thin    horny    scales 


Fig.  278.— Portiox  of  epidermis  from  a  sectiox  of  the  skix  of  the  finger, 
COLOURED  WITH  picrocarmixe.     (Ranvier.) 

a,  stratum  corneum;  b,  stratum  lucidum  with  flakes  of  kerato-hyalin;  c,  stratum 
granulosum,  the  cells  filled  with  drops  of  eleidin ;  d,  prickle-cells ;  e,  dentate 
projections  by  which  the  deepest  cells  of  the  epidermis  are  fixed  to  the  cutis  vera. 

which  eventually  become  detached  (fig.  279,  .s).  In  certain  parts  which 
have  a  thick  epidermis  and  are  not  covered  with  hair  {e.g.  the  palms 
and  soles),  the  superficial  part  of  the  epidermis  is  a  layer  mainly 
formed  by  a  number  of  greatly  swollen  cells  {sw),  forming  collectively 
what  has  been  termed  the  epitrichud  layer.  In  the  embryo  in  the 
second  and  third  month  of  intrauterine  life  it  covers  the  whole  body, 
but  is  thrown  off  where  hairs  are  developed. 

The  growth  of  the  epidermis  takes  place  by  a  multiplication  of  the 
cells  of  the  deeper  layers.  The  newly  formed  cells,  as  they  grow,  push 
towards  the  surface  those  which  were  previously  formed,  and  in  their 
progress  the  latter  undergo  a  chemical  transformation,  which  converts 
their  protoplasm  into  horny  material :  this  change  seems  to  occur  just 
at  and  above  the  stratum  granulosum  (see  fig.  278).  The  granules 
which  occupy  the  cells  of  the  stratum  granulosum  are  composed,  as 
already    stated,    of  a   substance   termed   eleidin,   which    according   to 


230 


THE   ESSENTIALS  OF   HI^OLOGY. 


Kanvier  becomes  chemically  altered  and  transformed  into  the  keratin  of 
the  more  superficial  strata. 

No  blood-vessels  pass  into  the  epidermis,  but  it  receives  nerves 
which  ramify  between  the  cells  of  the  rete  mucosum  in  the  form  of 
fine  varicose  fibrils  (fig.  279).  In  some  parts  these  are  enlarged  at 
their  extremity  and  along  their  course,  into  menisci  which  lie  between 


fir  (i  ^  ^- ,  --  ■:  - 


■A 


Fig.  279. — Sectiox  of  epidermis.     (Ranvier.) 

s,  superficial  homy  scales;  sio,  swollen  li6my  cells;  $.L,  stratum  lucidum ;  p,  prickle- 
cells,  several  rows  deep  ;  c,  elongated  cells  forming  a  single  stratum  near  the  coriuni ; 
$.pr,  stratum  granulosum  of  Langerhans,  just  below  the  stratum  lucidum.  Part 
of  a  plexus  of  nerve-fibres  is  seen  in  the  superficial  layer  of  the  cutis  vera.  From  this 
plexus  fine  varicose  nerve-fibrils  may  be  traced  passing  up  between  the  epithelium- 
ceUs  of  the  Malpighian  layer. 

the  deeper  epidermis  cells.  Such  terminations  are  seen  in  the  skin 
over  the  pig's  snout  (fig.  219)  and  in  the  root-sheaths  of  hairs.  They 
also  occur  in  the  skin  in  the  neighbourhood  of  the  entrance  of  the 
sweat-ducts  into  the  epidermis  (Ranvier)  (fig.  280). 

The  cutis  vera  or  corium  is  composed  of  dense  connective  tissue, 
which  becomes  more  open  and  reticular  in  its  texture  in  its  deeper 
part,  where  it  merges  into  the  subcutaneous  tissue.  It  is  thickest  over 
the  posterior  aspect  of  the  trunk,  whereas  the  epidermis  is  thickest  on 
the  palms  of  the  hands  and  soles  of  the  feet.  The  superficial  or 
vascular  layer  of  the  corium  bears  microscopic  papillos,  which  project  up 


THE   SKIN. 


231 


into  the  epidermis,  which  is  moulded  over  them.  These  papillae  for 
the  most  part  contain  looped  capillary  vessels,  but  some,  especially 
those  of  the  palmar  surface  of  the  hand  and  fingers,  and  the 
corresponding  part  of  the  foot,  contain  tactile  corpuscles,  to  which 
medullated  nerve-fibres  pass  (fig.  277). 

In  some  parts  of  the  body  (scrotum,  penis,  nipple,  and  its  areola), 
involuntary  muscular  tissue  occurs  in  the  deeper  portions  of  the  cutis 
vera,  and,  in  addition,  wherever  hairs  occur,  small  bundles  of  this  tissue 
are  attached  to  the  hair-follicles. 


fi.Kf^FMNSKl 


Fig.  280. — Section  of  the  skin  of  the  pulp  of  the  finger  of  a  child, 
stained  with  gold  chloride,  showing  nerves  terminating  in  an 
ivt-like  arborkscence  at  the  surface  of  the  cutis  vera  and  in  the 

DEEPEST    PART   OF   THE   EPIDERMIS.       (Ranvier.) 
p,   p,   outlines   of  iiapillse ;    vi,   n',   nerve-fibres   in   cutis   vera ;    m,   tei'minal  menisci ; 
If,  duct  of  a  sweat-gland. 

The  blood-vessels  of  the  skin  are  distributed  almost  entirely  to  the 
surface,  where  they  form  a  close  capillary  network,  sending  up  loops 
into  the  papillae  (fig.  281).  Special  branches  are  also  distributed  to  the 
various  appendages  of  the  skin,  viz.  the  sweat-glands  and  hair-follicles, 
with  their  sebaceous  glands  and  little  muscles,  as  well  as  to  the  masses 
of  adipose  tissue  which  may  be  found  in  the  deeper  parts  of  the  cutis. 

The  lymphatics  originate  near  the  surface  in  a  network  of  vessels, 
which  is  placed  a  little  deeper  than  the  blood-capillary  network.  They 
receive  branches  from  the  papillae,  and  pass  into  larger  vessels,  which 
are  valved,  and  which  run  in  the  deeper  or  reticular  part  of  the  corium. 
From  these  the  hmiph  is  carried  away  by  still  larger  vessels,  which 
course  in  the  subcutaneous  tissue. 

The   appendages   of  the   skin   are   the  nails,  the  haiis,  with  their 


232 


THE   ESSENTIALS   OF   HISTOLOGY. 


sebaceous  glands,  and  the  sweat-glands.     They  are  all  developed  as  thick- 
enings and  downgrowths  of  the  Malpighian  layer  of  the  epidermis. 

The  Nails. 
The  nails  are  thickenings  of  the  deeper  part  of  the  stratum  corneum 
developed  over  a  specially  modified  portion  of  the  skin  (fig.  282),  which 


r.m. 


Fig.    281. — Duct    of    a    sweat-gland   passing   through    the    epidermis. 
Magnified  200  diameters.     (Heitzmann.) 

J),  papillae  with  blood-vessels  injected;  r.m..,  rete  mucosum  Vjotween  the  papillse ;  c,  c, 
stratum  corneum ;  s.g.,  stratum  granulosum ;  d,  d,  sweat-duct  passing  through 
epidermis. 

is  known  as  the  bed  of  the  nail,  the  depression  at  the  posterior  part  of 
the  nail-bed  from  which  the  root  of  the  nail  grows  being  known  as  the 
nail-groove.  The  part  of  the  bed  which  occupies  the  inner  or  central 
portion  of  the  groove  is  termed  the  nail-matrix,  since  it  is  from  this  part 
that  the  growth  of  the  nail  proceeds.  The  distal  part  of  the  nail  forms 
the/jre  border,  and  is  the  thickest  part  of  the  body  of  the  nail.  The 
substance  of  the  nail  (fig.  283,  N)  is  composed  of  clear  horny  cells, 
each  containing  the  remains  of  a  nucleus  ;  it  rests  immediately  upon  a 
Malpighian  layer  {B)  similar  to  that  which  is  found  in  the  epidermis 
generally,  but  destitute  of  a  defined  stratum  granulosum.  Never- 
theless, in  the  more  superficial  cells  both  of  the  bed  and  matrix  there 
are  a  large  number  of  granules  to  be  seen,  which  appear  to  represent 
those  of  the  stratum  granulosum  of  the  epidermis.  These  granules 
are,  however,  not  composed  of  eleidin,  but  of  a  material  {onychogenic 
substance,  Kanvier)  which  stains  brown  instead  of  red  with  carmine  ; 
a  similar  material  occurs  in  the  cells  which  form  the  fibrous 
substance   and   cuticula   of  the   hairs.     The    corium   of  the   nail-bed 


i 


THE   NAILS. 

c         d 


233 


Fig.  282.— Longitudinal  section  thkough  the  root  ok  the  nail  and  its 

MATRIX.     Magnified  about  10  diameters. 

o,  root  of  nail ;  h,  Malpighian  layer  of  matrix  ;  c,  ridges  in  dermis  of  nail-bed  ;  d,  epitrichial 

layer  of  epidermis  ;  e,  cponychium  ;  /,  bone  (termijial  phalanx)  of  finger. 


Fig.  283. 


-Section  ACiiosb  the  nail  and  nail-bed      Magnified  100  diameters. 
(Heitzmann.) 
P,  ridges  with  blood-vessels  ;  B,  rete  mucosum  ;  N,  nail. 


234 


THE   ESSENTIALS   OF  HISTOLOGY. 


is  beset  with  longitudinal  ridges  instead  of  the  papillae  which  ai'e 
present  over  the  rest  of  the  skin ;  these,  like  the  rest  of  the  superficial 
part  of  the  corium,  are  extremely  vascular. 

The  nail-bed  also  receives  many  nerve-fibres,  some  of  which  end  in 
Pacinian  corpuscles  whilst  others  ramify  in  the  ridges  of  the  corium, 
and  others  again  penetrate  amongst  the  deeper  epithelium  cells. 

The  nails  are  developed  in  the  foetus  at  about  the  third  month,  the 
groove  being  formed  at  this  time  in  the  corium,  and  the  nail  rudiment 
appearing  in  it  as  a  thickening  of  the  stratum  lucidum,  which  lies  over 
the  bed.  It  becomes  free  in  the  sixth  month,  its  free  end  being  at  first 
thin,  but  as  it  grows  forward  over  the  bed  it  receives  additions 
on  its  under  surface — at  least  in  the  posterior  part  of  the  bed — so  that 
after  a  time  the  distal  end  becomes  thicker.  The  epitrichial  layer  of 
the  cuticle  which  originally  covered  the  developing  nail  becomes 
detached  after  the  fifth  month,  and,  after  birth,  only  remains  as  the 
narrow  border  of  cuticle  (ejwnychiurn)  which  overlies  the  lunula  at  the 
root. 

Hairs. 

The  hairs  are  growths  of  the  epidermis,  developed  in  little  pits — 
the  hair-follicles — which  extend  downwards  into  the  deeper  part  of  the 

corium,  or  even  into  the  subcutaneous 
tissue.  The  hair  grows  from  the 
bottom  of  the  follicle,  the  part  which 
thus  lies  within  the  follicle  being 
known  as  the  root  (fig.  285). 

The  substance  of  a  hair  is  mainly 
composed  of  a  pigmented,  horny, 
fibrous  material  (fig.284, /),  which  can 
be  separated  by  the  action  of  sul- 
phuric acid  into  long  tapering  fibril- 
lated  cells,  the  nuclei  of  which  are 
still  visible.  The  fibrous  substance 
of  the  hair  is  covered  by  a  layer 
of  delicate  imbricated  scales,  termed  the  hair-cuticle  (c).  In  many 
hairs,  but  not  in  all,  the  centre  is  occupied  by  an  axial  substance 
{medulla,  m),  formed  of  angular  cells  which  contain  granules  of  eleidin, 
and  frequently  have  a  dark  appearance  from  the  presence  of  minute 
air-bubbles.  The  latter  may  also  occur  in  interstices  in  the  fibrous 
substance.  When  they  are  present,  the  hair  looks  white  by  reflected 
light.  The  root  has  the  same  structure  as  the  body  of  the  hair,  except 
at  its  extremity,  which  is  enlarged  (fig.  285) ;  this  enlargement  is  com- 


FiG.  284. — Piece  of  human  hair. 
Magnified. 

A,  seen  from  the  surface  ;  B,  in  optical 
section,  c,  cuticle ;  /,  fibrous  sub- 
stance ;  in,  medulla,  the  air  having 
been  expelled  by  Canada  balsam. 


THE   HAIRS. 


235 


posed  mainly  of  soft,  growing  cells,  and  fits  over  a  vascular  j^o^pi^ld, 
which  projects  up  into  the  bottom  of  the  follicle  (fig.  287). 

Structure  of  hair-follicle  (figs.  28.5  to  288). — The  follicle,  like  the  skin 
itself,  of  which  it  is  a  recess,  is  composed  of  two  parts  :  one  epithelial, 
and  the  other  connective-tissue.  The  epithelial  or  epidermic  part  of 
the  follicle  closely  invests  the  hair-root,  and  is  often  in  great  part 
dragged  out  with  it ;  hence  it  is  known  as  the  root-sheath.  It  consists 
of  an    outer  layer  of  soft    columnar  and    polyhedral   cells,   like    the 


eijidermis 


junction  of  inner  and 
outer  root-sheaths 


medulla 

fibrous  substance 


Fig.  285. 


papilla 

blood-vessels 
-Diagram  to  explain  the  formation  of  a  hair. 


(Maurer.) 

Malpighian  layer  of  the  epidermis,  but  without  stratum  granulosum — 
the  outer  root-sheath  ;  and  of  an  inner,  thinner,  horny  stratum  next 
to  the  hair — the  inner  root-sheath.  The  inner  root-sheath  itself  consists 
of  three  layers,  the  outermost  being  composed  of  horny,  fibrous,  oblong 
cells  the  nuclei  of  which  are  obscure  and  difficult  to  make  out  (Henle's 
layer),  the  next  of  polyhedral  nucleated  cells  containing  eleidin  {Huxley's 
layer),  and  the  third — the  cuticle  of  the  root-sheath — a  layer  of  down- 
wardly imbricated  scales,  which  fit  over  the  upwardly  imbricated  scales 
of  the  hair  itself.  In  the  more  superficial  part  of  the  hair-follicle  the 
layers  of  Huxley  and  Henle  are  indistinguishable,  the  cells  of  both 


236 


THE   ESSENTIALS   OF   HISTOLOGY. 


being  clear  and  keratinised ;  even  lower  down  where  distinguishable 
they  show  a  tendency  to  dovetail  into  one  another.  At  the  bottom 
of  the  follicle  no  differentiation  into  layers  can  be  made  out  in  the 
root-sheath,  which  is  here  formed  by  a  uniform  mass  of  soft  cells 
surrounding  the  papilla. 


hy.  - 


//.:■ 


.--iv 


Fig.  286.— Sfx'tions  acros.s  hair-follicles  from  the  scalp  of  an  infant. 

I.  Through  papilla.  II.  Just  above  papilla.  III.  About  middle  of  follicle.  IV.  Near 
outer  part  of  follicle.  In  I.  :—p,  papilla ;  c,  eiiithelium  .surrounding  papilla,  with 
pigment  in  cells ;  A?/,  hyaline  layer  of  dermic  coat  with  thin  outer  root-sheath  just 
within  it.  In  II.,  III.,  IV.  :— o,  outer  root-sheath;  i' ,  layer  of  Ilenle  and  i",  layer 
of  Huxley  of  the  inner  root-sheath  ;  c,  cuticle  of  root-sheath  ;  h,  hair. 

In  the  greater  extent  of  the  follicle  the  outer  root-sheath  is  several 
layers  deep,  but  as  the  bottom  of  the  follicle  is  approached  it  becomes 
thinner  and  is  finally  reduced  to  a  single  stratum  of  cells  which  becomes 
flattened  out  into  a  very  thin  layer  in  the  papillary  part  (fig.  286,  I.). 

The  connective  tissue  or  dermic  part  of  the  hair-follicle  is  composed 
internally  of  a  vascular  layer,  which  is  separated  from  the  root-sheath 


THE   HAIES. 


237 


by  a  basement-membrane  termed  the  hyaline  layer  of  the  follicle.  This 
inner  vascular  layer  corresponds  to  the  superficial  layer  of  the  cutis 
vera.     Its  fibres  and  cells  have  a  regular  circular  arrangement  around 


Fig.  287.— Longitudinal  section  of  a  hair-follicle.     Magnitied  200  diameters. 
0,  outer;  i,  inner  root-sheath  ;  /;,  hair  ;  x,  part  shown  magnified  in  fig.  28S. 


the  follicle,  the  cells  being  flattened  against  the  hyaline  layer.  Exter- 
nally the  dermic  coat  of  the  follicle  has  a  more  open  texture,  correspond- 
ing to  the  deeper  part  of  the  cutis,  and  contains  the  larger  branches 
of  the  arteries  and  veins.     In  the  large  tactile  hairs  of  animals,  the 


238 


THE   ESSENTIALS  OF  HISTOLOGY. 


Fig.  288. — A  small  portion  of  the  section  shown  in  fig.  287  enlarged 

TO  exhibit  the  structure  of  the  several  layers. 

h,  hair ;  c",  its  cuticle ;  <;',  cuticle  of  root-sheath  ;  i",  Huxley's  layer ;  i',  Henle's  layer ; 

o,  outer  root-sheath  ;  hy,  hyaline  layer ;  d,  dermic  coat ;  J]  fat-cells. 


Fig.  289. — Nerves  and  nerve-endings  in  the  skin  and  hair-follicles. 
(G.  Retzius.) 
list,  horny  stratum  ;  rm,  rete  Malpighii ;  c,  superficial  nerve-fibre  plexus  in  the  cutis  ; 
71,  cutaneous  nerve  ;  is,  inner  root-sheath  of  hair  ;  as,  outer  root-sheath  ;  h,  hair  ;  dr, 
sebaceous  glands. 


THE   HAIRS. 


239 


veins  near  the  bottom  of  the   follicle  are  dilated  into  sinuses,  so  as 
to  produce  a  kind  of  erectile  structure. 

The  hair-follicle  receives  nerve-tibres  which  pass  into  the  papilla,  and 
others  which  enter  the  root-sheath.  These  last  are  derived  from  the 
supei-ficial  nerves  of  the  corium  and  form  ring-like  arborisations  in  the 
upper  part  of  the  hair  follicle.  They  are  especially  well  developed  in 
the  large  tactile  hairs  (whiskers)  of  animals  (figs.  289,  290,  291). 


Fig.  290. — From  a  section  of  skin  pbbpared  by  the  chromate  of  silver 
method,  showing  the  upper  part  of  two  hairs  and  the  terminal 
arborisations  of  nerve-fibees  in  their  root-sheaths.  (van 
Gehuchten.) 

The  hair  grows  from  the  bottom  of  the  follicle  by  multiplication 
of  the  soft  cells  which  cover  the  papilla,  these  cells  becoming  elongated 
and  pigmented  to  form  the  fibres  of  the  fibrous  substance,  and  other- 
wise modified  to  produce  the  medulla  and  cuticle  of  the  hair  and  the 
several  layers  of  the  root-sheath.  The  cells  which  form  the  medulla 
of  the  hair  and  the  inner  root-sheath  are  filled  with  granules  of  eleidin, 
but  those  which  form  the  fibrous  substance  and  cuticula  of  the  hair 
have  granules  which  stain  brown  with  carmine,  and  appear  similar  to 
those  which  are  met  with  in  the  corresponding  cells  of  the  nail-matrix 
(Ranvier)  (see  p.  232). 

On  the  side'  to  which  the  hair  slopes  a  small  patch  of  richly  innervated 
thickened  epidermis  is  usually  to  be  found,  developed  over  an  enlarged 
papilla  of  the  cutis  vera  :  while  on  the  opposite  side  of  the  hair  is  a  flat  area 
of  skin  with  thickened  scale-like  ejiiderniis,  which  may  repres^ent  a  vestige 
of  the  rej3tilian  scale  (Pinkus). 


240 


THE   ESSENTIALS   OF   HISTOLOGY. 


The  hair  germs  when  they  first  appear  (as  at  a,  fig.  293)  are  singularly 
like  certain  tactile  patches  which  are  found  in  the  skin  of  amphibia  and  some 
reptiles,  and  it  is  possible  that  hairs  have  become  developed  phylogenetically 
.from  these  patches.  It  is  well  known  that  the  tactile  sensibility  of  many 
parts  of  the  skin  is  intimately  associated  with  the  hairs,  where  these 
occur,  although  parts  devoid  of  hairs  mav  also  have  a  highly  developed 
sense  of  touch. 

Besides  the  hair-follicles  already  described,  which  are  provided  with 
a  papilla,  from  the  cells  on  the  surftice  of  which  the  hair  and  its  inner 
root-sheath  grow  {growing  hairs,  pupillated  hairs,  hairs  with  hollow  bulb), 


u. 


Fig.  291. — Nkrve  ending  in  outer  root-she.'^th  of  t.\ctile  hair  ov  e.vbbit. 

(Ranvler.) 

n,  nerve-fibre  ;  m,  tactile  meniscus  ;  o,  outer  root-sheath  ;  i,  inner  root-sheath  ;  h,  hair  ; 

hy,  hyaline  membrane. 


there  are  many  hairs  which  are  unprovided  with  a  papilla  and  the 
follicle  of  which  ceases  at  the  level  of  attachment  of  the  arrector 
pili  muscle  {dub-hairs,  non-papillated  hairs,  hairs  with  solid  bulb).  These 
are  hairs  which  have  lost  their  papilla  and  have  ceased  to  grow  ;  they 
are  more  easily  eradicated  than  the  growing  hairs,  and  tend  to  fall  out 
spontaneously  after  a  time.  In  their  follicles  the  whole  of  the  lower 
part,  including  the  original  papilla  and  the  soft  growing  cells  which 
cover  it,  have  entirely  disappeared,  the  hair  being  now  attached  at  its 
sides  and  below  to  the  root-sheath.  A  hair  which  has  thus  ceased  to 
grow  eventually  becomes  lost,  but  its  place  is  presently  supplied  by  a 
new  hair,  which  becomes  developed  in  a  down-growth  from  the  bottom 
of  the  follicle,  a  new  papilla  becoming  formed  at  the  extremity  of  the 


THE   HAIRS. 


241 


down-growth   (fig.   292).     If  not  previously  detached,  the  old  hair  is 
pushed  out  from  the  follicle  by  the  one  which  replaces  it. 

The  detachment  of  the  non-papillated  hairs  is  preceded  by  an  absorp- 
tion of  the  root  of  the  hair  and  of  the  investing  inner  root-sheath. 


]  *  >j.-< 


^     '2    *c,^ 


Fig.  292.— Loxgitudinal  section  through  the  follicle  of  a  hair  which 

HAS   ceased   to   grow   AND   THE   ROOT   OF   WHICH   IS   UNDERGOING  ABSORP- 
TION.    Magnified  200  diameters. 

This  absorption  appears  to  be  effected  by  the  cells  of  the  outer  sheath, 
which  multiply  at  the  expense  of  the  keratinised  parts  of  the  hair  root 
and  thus  undermine  its  attachment  to  the  follicle  (fig.  292). 

The  hairs  are  originally  developed  in  the  embryo  in  the  form  of 
small  solid  down-growths  from  the  Malpighian  layer  of  the  epidermis 
(fig.  293).  The  haii'-germ,  as  it  is  called  (although  it  gives  rise  not 
only  to  the  hair  proper  but  to  the  epithelium-cells  of  the  hair-follicle 


242  THE   ESSENTIALS   OF   HISTOLOGY. 

also),  is  at  first  composed  entirely  of  soft  growing  cells,  the  outermost 
and  deepest  having  a  columnar  shape  :  but  presently  those  in  the 
centre  become  differentiated,  so  as  to  produce  a  minute  hair  invested 
by  inner  root-sheath,  its  base  resting  upon  a  papilla  which  has  become 
inclosed  by  the  extremity  of  the  hair-germ  and  which  is  continuous 
with  the  connective  tissue  of  the  corium  (figs.  294,  295).  As  the  minute 
hair  grows,  it  pushes  its  way  through  the  layers  of  the  epidermis, 
w^hich  it  finally  perforates,  the  epitrichial  layer  being  thrown  off 
(p.  229).  At  the  same  time  the  follicle  grows  more  deeply  into  the 
cutis  vera,  carrj'ing  the  papilla  down  with  it. 


Fig.  293.— Hair-germs  ix  a  .section  of  the  .scalp  of  a  HUJtAX  fcetus. 
(Szymonowicz.)     Magnified  230  diameters. 

a,  commencing  down-growth  of  epidermis  ;  4,  further  stajje  of  down-growth ;  c,  connec- 
tive-tissue cells  beginning  to  accumulate  to  produce  the  dermic  coat  of  the  follicle  ; 
d,  hair-follicle  more  advanced  in  development ;  e,  section  of  a  blood-vessel. 

The  hair-rudiments  begin  to  appear  at  the  third  or  fourth  month  of 
foetal  life  ;  their  growth  is  completed  about  the  fifth  or  sixth  month, 
and  the  fine  hairs  which  they  form  constitute  a  complete  hairy  cover- 
ing termed  the  lanugo.  This  is  entirely  shed  within  a  few  months  of 
birth,  the  neAv  hairs  being  formed  in  down-growths  from  the  old  hair- 
follicles  in  the  manner  already  mentioned. 

Hairs  grow  at  the  rate  of  half  an  inch  per  month.  They  are  found 
all  over  the  surface  of  the  body  except  on  the  palms  of  the  hands  and 
the  soles  of  the  feet,  and  on  the  distal  phalanges  of  the  fingers 
and  toes.  They  usually  slant,  and  in  the  negro  the  hair-follicles 
are  even  considerably  curved.  On  the  scalp  they  are  set  in  groups, 
as  is  well  seen  in  a  horizontal  section. 

The  hairs  of  animals  are  often  curiously  marked  by  the  arrangement  of 
their  medulla,  the  markings  being  characteristic  of  particular  species. 
In  some  animals,  e.g.  the  mole,  the  hairs  have  a  varicose  form  with  alter- 
nate enlargements  and  constrictions.     In  human  hair  tlie  disappearance  of 


GROWTH  OF  THE   HAIRS. 


243 


the  papilla  is  preceded  by  its  <,a-adiial  diiiiiimtioii  in  size,  and  during  this 
period  the  root  of  the  hair  is  becoming  gradually  more  slender'  (Ranvier), 
so  that  when  sucli  a  hair  is  pulled  out  it  appears  to  be  of  least  diameter 
near  the  bulb,  instead  of  being  largest  there,  as  is  the  case  under  ordinary 
circumstances. 

Muscles  of  the  hairs. — A  small  muscle  composed  of  bundles  of 
plain  muscular  tissue  is  attached  to  each  hair-follicle  {arredoi-  pili)  ; 
it  passes  from  the  superficial  part  of 
the  corium,  on  the  side  to  which  the 
hair  slopes,  obliquely  downwards,  to 
be  attached  near  the  bottom  of  the 
follicle  to  a  projection  formed  by  a 
localised  hypertrophy  of  the  outer 
root-sheath.  When  the  muscle  con- 
tracts, the  hair  becomes  more  erect, 
and  the  follicle  is  dragged  upwards  so 
as  to  cause  a  prominence  on  the 
general  surface  of  the  skin,  whilst 
the  part  of  the  corium  from  which 
the  little  muscle  arises  is  correspond- 
ingly depressed ;  the  roughened  con- 
dition known  as  '  goose  skin '  being 
in  this  way  produced.  There  is 
always  a  sebaceous  gland  in  the 
triangle  formed  between  the  arrector 
pili,  the  mouth  of  the  hair-follicle, 
and  the  epidermis,  so  that  the  con- 
traction of  the  arrector  generally 
causes  the  secretion  of  the  gland  to 
be  extruded. 


Glands  of  the  Skin. 


Fig.  294.— Developing  hair  from 
humax  embryo  of  4^  months. 
(Ranvier. ) 

The    sebaceous    glands   (fi^.   285)   are    P,  Papilla,/,  hair-rudiment;  ^  cells  from 
.jv^uu.'^v^^/u^    e,xuu.u»   \"o-   -    "/   ""-^        which  the  inner  root-sheath  is  becom- 


small  saccular  glands,  the  ducts  from 

which    open  into   the  mouths  of  the 

hair-follicles,  but  they  are  also  found 

in  a  few  situations  which  are  devoid 

of  hairs  (margin  of  lips,  labia  minora, 

glans,  and  prepuce).     The  Meibomian 

glands   of  the    eyelid  may  also  be    regarded   as   modified   sebaceous 

glands.      Both   the  duct  and   the  saccules   are   lined  by  epithelium, 

which  becomes  charged  with  fatty  matter.     This  sebaceous  matter  is 


ing  formed  ;  k,  keratiiiised  part  of  inner 
root-sheath,  uncoloured  by  carmine  ;  o, 
outer  root-sheath  ;  6,  epithelial  projec- 
tion for  insertion  of  arrector  pili ;  s, 
sebaceous  gland  ;  t,  sebaceous  degenera- 
tion of  cells  in  the  part  which  will 
become  the  neck  of  tlie  follicle.  This 
forms  a  channel  for  the  passage  of  the 
hair-point  through  the  Malpighian 
laver. 


244 


THE   ESSENTIALS  OF   HISTOLOGY. 


discharged  into  the  cavity  of  the  saccule,  probably  owing  to  the 
disintegration  of  the  cells  within  which  it  is  formed.  There  may  be 
more  than  one  sebaceous  gland  attached  to  each  hair-follicle. 

The  sebaceous  glands  are  developed  as  outgrowths  from  the  outer 
root-sheath  (figs.  294,  295,  s). 


[: 


WM$M 


^^h 


I  ^.-• 


Fig.  295.— Loxgitudixal  sectiox  of  a  haik  with  its  follicle  from  a 
six-JiON'THs'  HCMAX  EMBRYO.  (Szymonowicz. )  Magnified  about  150 
diameters. 

p,  papilla  ;  h,  young  hair ;  ;',  inner  root-sheath ;  d,  dermic  coat  of  follicle  ;  o,  outer  root- 
sheath  ;  «,  sebaceous  gland  rudiment ;  6,  projection  for  insertion  of  arrector  pili. 

The  sweat-glands  are  abundant  over  the  whole  skin,  but  they  are 
most  numerous  on  the  palm  of  the  hand  and  on  the  sole  of  the 
foot.  They  are  composed  of  coiled  tubes,  which  lie  in  the  deeper 
part  of  the  integument  and  send  their  ducts  up  through  the   cutis 


SWEAT-GLANDS. 


24r 


to  open  on  the  surface   by  corkscrew-like  channels   in   the  epidermis 
(tigs.   276,  281). 

The  glandular  or  secreHng  tube  is  a  convoluted  tube  composed  of  a 
basement-membrane  lined  by  a  single  layer  of  cubical  or  columnar  epi- 
thelium-cells, and  with  a  layer  of  longitudinally  or  obliquely  disposed 
tibres  between  the  epithelium  and  basement-membrane  (fig.  296).  These 
fibres  are  usually  regarded  as  muscular,  but  the  evidence  on  this  point 
is  not  conclusive.  The  secreting  tube  is  considerably  larger  than  the 
efferent  tube  or  duct,  which  begins  within  the  gland  and  usually  makes 
several  convolutions  before  leaving  the  gland  to  traverse  the  cutis  vera. 


^ 


Fig.  29G. — Section'  of  a  sweat-glaxd  in  the  skin  of  man. 

a,  a,  secreting  tube  in  section  ;  h,  a  cuil  seen  from  above ;  c,  c,  efferent  tube  ; 
d,  intei-tubular  connective  tissue  with  blood-vessels.  1,  basement-membrane  ; 
2,  muscular  fibres  cut  across  ;  3,  secreting  epithelium  of  tubule. 

The  efferent  tube  has  an  epithelium  consisting  of  two  or  three  layers  of 
cells,  within  which  is  a  well-marked  cuticular  lining,  but  there  is  no 
muscular  layer.  The  passage  through  the  epidermis  has  no  proper  wall, 
but  is  merely  a  channel  excavated  between  the  epithelium-cells.  Very 
large  sweat-glands  occur  in  the  axilla. 

The  ceruminous  cjlavds  of  the  ear  (fig.  297;  are  modified  sweat-glands. 
The  secretion  is  of  a  sebaceous  nature,  instead  of  being  watery  like 
that  of  the  ordinary  sweat-glands. 

The  sweat-glands  are  developed,  like  the  hairs,  from  down-growths 
of  the  Malpighian  layer  of  the  epidermis  into  the  corium.  They  are 
distinguishable  from  the  hair-germs  by  the  fact  that  the  cells  of  the 
outermost  layer  are  not  columnar  in  shape,  but  spheroidal  or  poly- 


246 


THE   ESSENTIALS   OF   HISTOLOGY. 


hedral.  The  sweat-gland  germs  which  are  thus  formed  become 
eventuall}'  coiled  up  at  their  extremities  and  converted  into  hollow 
tubes.  The  muscular  fibres  of  the  tubes  as  well  as  the  secretin  "• 
epithelium- cells  are  ectodermic  structures. 

The  sweat-glands  receive  nerve-fibres,  and  each  gland  has  a  special 
cluster  of  capillary  blood-vessels. 


Root-sbeatb  of  1 
folUcle.  / 


Root  of  hair. 


Sebaceous  glands. 


Hair-follicle. 


Cenimiijous  gland. 


Fig.  297.— Section  of  skin  of  acditoby  meatt.s,  ixclcdixg  two  hair- 
follicles  WITH  THEIK  .SEBACEOUS  GLANDS  ANT)  TWO  CEKUMINOCS  GLANDS. 
(Griiber.) 


The  MAinLVRY  Gl.a:nd.s. 

The  mammary  glands  are  compound  racemose  glands  which  open 
by  numerous  ducts  upon  the  apex  of  the  nipple.  The  ducts  are 
dilated  into  small  reservoirs  just  before  reaching  the  nipple.  If 
traced  backwards,  they  are  found  to  commence  in  groups  of  saccular 
alveoli  (fig.  298).     The  walls  of  the  ducts  and  alveoli  are  formed  of 


THE   MAMMARY   GLANDS. 


247 


Fig.  298.— Section   of   mammary   gland   of   woman  during   lactation. 
(Testut,  after  de  Sinetv.) 

a,  lobule  of  gland  ;  6,  acini  lined  by  cubical  epithelium  ;  c,  duct ;  t,  connective-tissue 

stroma. 


.,..f;^^^''^, 


Fig.  299.— Section  of  jiammart  gland,  human,  in  full  activity. 

(v.  Ebner. )     x  110. 

a,  a',  a",  alveoli  variou.sly  cut,  and  distended  by  secretion  ;  g,  if ,  commencing  ducts  ; 

i,  connective  tissue. 


248 


THE   ESSENTIALS   OF   HISTOLOGY. 


a  basement-membrane  lined  by  a  simple  layer  of  flattened  epithelium 
(fig.  299).  Milk  globules  may  be  seen  within  the  alveoli  and  ducts, 
and  at  the  commencement  of  lactation  amoeboid  cells  containing 
fat-particles  appear  in  the  secretion  {colostrum  corj)usdes).     These  are 


N^^ 


Fig.  300. — Ax  alveolus  with  fat-drops  ix  cells,    (v.  Ebner.)     x360. 

<,  cells  of  alveolus ;  k,  cells  forming  basket-like  basement  membrane,  wt ;  i,  connective 

tissue. 


Fig.  301.— Sectiox  from  the  same  gland  as  that  shown  in  fig.  299. 
(v.  Ebner.       x  110. 


b,  connective  tissue ;    d,  undeveloped  alveoli ;   d',  partially  developed  alveoli  ; 
g,  blood-vessels ;   m,  portion  of  larger  duct  with  two-layered  epithelium. 


MAMMARY  GLANDS. 


249 


probably    emigrated    leucocytes    similar  to    the    salivary    corpuscles 

of  saliva,    but   some   have   been   looked  upon  as  epithelium-cells  or 

portions   of  epithelium-cells  which   have  become    detached    from    the 
general  linins;  of  the  alveoli. 


Fig.    302.— SeCTIOX   of   DKVELOPING   JrAMilART   GL.iXD  OF   HORSE. 

(C.  Hamburger.) 
V,  bloo(J-ve8sels  ;  s,  sebaceous  glands. 

Development. — The  mammary  glands  are  developed  in  the  same 
manner  as  the  sweat-glands,  excepting  that  the  secreting  part  does  not 
become  convoluted  and  tubular.  In  the  virgin  mamma  they  show 
A'ery  few  and  small  groups  of  alveoli,  but  as  pregnancy  advances 
the  gland  ducts  bud  out  extensively,  and  many  more  alveoli  are  formed 
and  undergo  enlargement,  until  the  greater  part  of  the  connective  tissue 
in  the  mammary  region  is  permeated  by  them.  In  sections  of  the 
gland  they  may  be  seen  in  various  stages  of  development  (figs.  299, 
301).     After  lactation  is  over  they  undergo  a  process  of  retrogres.sion. 


250  THE   ESSENTIALS  OF   HISTOLOGY. 


LESSON    XXVI. 
STRUCTURE  OF  THE  HEART. 

1.  In  sections  through  the  wall  of  the  auricle  note  the  relative  thickness  of 
the  epicardium,  myocardium,  and  endocardium.  Observe  the  blood-vessels 
and  nerve-fibres  under  the  epicardium,  often  embedded  in  fat  ;  here  and 
there  a  ganglion  may  be  seen  under  this  membrane.  Notice  also  the  elastic 
networks  under  both  the  pericardium  and  endocardium.  Make  a  general 
sketch  from  this  section. 

2.  In  sections  through  the  wall  of  the  ventricle  the  same  points  are  to  be 
noticed.  The  muscular  fibres  are  variously  cut.  In  those  which  are  cut 
longitudinally,  the  branching  of  the  filires  and  their  union  both  laterally 
and  by  their  branches  may  be  seen.  Notice  also  that  although  the  fibres 
are  cross-stiiated  this  is  less  distinct  than  in  voluntary  muscle,  and  that  the 
nuclei  lie  near  the  centre  of  each  fibre.  Transverse  markings  may  also  be 
seen  passing  across  the  fibres  between  the  nuclei  ;  this  is  usually  taken  as 
indicating  a  division  into  cells.  The  endocardium  is  very  thin,  especially 
over  the  columnse  carnepe. 

3.  Section  through  one  of  the  valves  of  the  heart. ^ 

4.  If  a  portion  of  endocardium  of  the  sheep's  heart  is  spread  out  on  a  slide 
and  examined  in  salt  solution,  a  network  of  large  beadetl  fibres  may  be  seen 
with  a  low  power  or  even  with  a  lens  ;  they  are  also  well  seen  in  sections. 
These  are  the  fibres  of  Purkinje  ;  they  are  formed  of  large,  square-looking 
cells,  usually  containing  two  nuclei,  and  having  striated  muscular  substance 
at  their  periphery.     The  fibres  of  Purkinje  may  also  be  seen  in  sections. 

5.  The  lymphatics  of  the  heai't  may  be  injected  with  Berlin  blue  by 
sticking  the  nozzle  of  the  injecting  syringe  into  the  muscvdar  substance,  in 
the  interstices  of  which  the  lymphatics  arise.  These  commencing  lymphatics 
lead  to  efferent  vessels  which  pass  undei'  the  epicardium  towards  the  base 
of  the  heart. 

6.  The  epithelium  which  covers  the  epicardium,  and  that  which  lines  the 
endocardium,  may  be  studied  in  preparations  of  the  fresh  organ  which  have 
been  well  rinsed  with  distilled  water  ;  tlien  treated  with  nitrate  of  silver, 
again  rinsed,  and  subsequently  exposed  to  the  light  and  hardened  in  alcohol. 
Surface  sections  are  to  l^ie  made  and  mounted  in  xylol  balsam  or  dammar. 


The  muscular  tissue  of  the  heart  {myocardium)  forms  the  main 
thickness  of  the  ventricles  and  also  of  parts  of  the  auricles.  It  is 
composed  of  a  network  of  fibres  which  are  formed  of  uninucleated 
transversely  striated  cells,  the  structure  of  which  has  already  been 
studied  (Lesson  XVII.  p.  124). 

^  The  appearances  which  are  to  be  studied  in  sections  1,  2,  and  3  can  all  be 
obtained  in  one  preparation,  viz.  a  vertical  section  including  a  portion  of  auricle 
and  ventricle  and  a  flap  of  the  intervening  auriculo-ventricular  valve. 


STRUCTURE   OF  THE   HEART. 


251 


In  the  interstices  ot"  the  muscular  l)uiulle3  there  is  a  little  areolar 
tissue  in  which  run  the  very  numerous  blood-capillaries  and  the 
lacunar  lymphatics. 


7C/ 


h-^'m 


Fig.  303  a,  b. 


Fig.  303  c. 


I 


Fig.  303  a,  b.  —Section"  of  the  right  auricle. 

A,  Epicardium  and  adjacent  part  of  the  myocardium,     n,  serous  epithelium  in  section; 

b,  connective-tissue  layer ;  c,  elastic  network ;  d,  subserous  areolar  tissue  ;  e,  fat ; 
;■,  section  of  a  blood-vessel ;  tj,  a  small  ganglion ;  k,  musculajr  fibres  of  the 
myocardium  ;  i,  intermuscular  areolar  tissue. 

B,  Endocardium  and  adjacent  layer  of  the  myocardium,     a,  lining  epithelium ;  6,  con- 

nective tissue  with  fine  elastic  fibres ;  c,  layer  with  coarser  elastic  fibres ;  d,  sub- 
endocardial connective  tissue  continuous  with  the  intermuscular  tissue  of  the 
myocardium ;  h,  muscular  fibres  of  the  myocardium  ;  m,  plain  muscular  tissue  in 
the  endocardium. 

Fig.  303  c— Section  through  one  of  the  flap.s  of  the  .\ortic  valve,  and 

PART  of   the   CORRE-SPONDING    SINU.S    OF    VALSALVA,    WITH    THE   ADJOINING 
PART   OF   THE   VENTRICULAR    WALL.       (Horslej.) 

a,  endocardium,  prolonged  over  the  valve  ;  6,  sub-cndocardial  tissue  ;  c,  fibrous  tissue 
of  the  valve,  thickened  at  c'  near  the  free  edge ;  d,  section  of  the  lunula  ;  e,  section 
of  the  fibrous  ring  ;  /',  muscular  fibres  of  the  ventricle  attached  to  it ;  g,  loose 
areolar  tissue  at  the  base  of  the  ventricle ;  s.  V.  sinus  of  Valsalva ;  1,  3,  3,  inner, 
middle,  and  outer  coats  of  the  aorta. 


252  THE   ESSENTIALS   OF   HISTOLOGY. 

The  myocardium  is  covered  externall}^  by  a  layer  of  serous  mem- 
brane— the  epicardiuin  (cardiac  pericardium  fig.  303,^) — composed, 
like  other  serous  membranes,  of  connective  tissue  and  elastic  fibres, 
the  latter  being  most  numerous  in  its  deeper  parts.  Underneath  the 
epicardium  run  the  blood-vessels,  nerves,  and  lymphatic  vessels  of  the 
heart  embedded  in  areolar  and  adipose  tissue,  this  tissue  being  con- 
tinuous with  that  which  lies  between  the  muscular  bundles ;  the  free 
surface  of  the  membrane  is  covered  by  serous  epithelium. 

The  endocardium  (fig.  303,  B)  has  a  structure  not  very  unlike  the 
pericardium.  It  is  lined  by  a  pavement-epithehum  (endothelium), 
like  that  of  a  serous  membrane,  and  consists  of  connective  tissue  \y\l\\ 


Fig.  304.— Fragment  of  the  xetwork  of  Purkixje's  fibres  from  the 

VENTR1CUL.\R   EXDOCARDIUJI   OF   THE   SHEEP.       (Rauvjer.) 
c,  clear  cell  bod}-;  n,  nuclei;  /,  striated  fibrils. 

elastic  fibres  in  its  deeper  part,  between  which  there  may,  in  some 
parts,  be  found  a  few  plain  muscular  fibres.  Fat  is  sometimes  met  with 
under  the  endocardium. 

In  some  animals,  e.g.  the  sheep  and  ox,  large  beaded  fibres  are 
found  under  the  endocardium.  These  are  formed  of  clear  cells  joined 
both  end  to  end  and  laterally,  and  generally  containing  in  their  centre 
two  nuclei,  Avhilst  the  peripheral  part  of  the  cell  is  formed  of  cross- 
striated  muscular  tissue  ;  the  chains  of  cells  form  the  fibres  of  Purldnje 
(fig.  304).  They  appear  to  be  cardiac  cells  which  have  undergone 
differentiation  into  striated  muscle  substance  only  at  their  periphery, 
the  non-difterentiated  part  of  the  cell  having  continued  to  grow  until  it 
has  attained  a  considerable  size.  In  man  distinct  fibres  of  Purkinje 
are  not  seen,  but  the  innermost  muscular  fibres  of  the  ventricles  are 
larger  than  those  which  lie  more  externally :  they  also  undergo 
development  somewhat  later  (J.  B.  MacCallum). 

A  muscular  bundle  which  shows  less  differentiation  than  the  rest  of  the 
cardiac  muscle  has  been  described  by  Stanley  Kent,  His  and  others,  running 


STRUCTURE   OF  THE   HEART.  253 

in  the  septum  and  affonling  a  bridging  connexion  between  the  muscle  of  the 
auricles  and  that  of  "the  ventricles.  This  bundle  is  commonly  believed  to 
serve  to  propagate  the  contractions  of  the  auricles  to  the  ventricles  and  thus 
to  maintain  their  regularity  of  ihythra  ;  and  it  is  stated  that  when  the 
bundle  in  question  is  severed  experimentally  or  by  disease  this  propagation 
is  no  longer  possible,  and  the  ventricles  in  consequence  beat  with  a  much 
slower  rhythiu  than  the  auricles.  The  accuracy  of  this  statement  is,  however, 
denied  by  Kronecker,  who  regards  the  regularity  of  the  cardiac  contractions 
as  a  function,  not  of  the  muscular  substance  of  the  heart,  but  of  the  nerve- 
fibres,  which  are  distributed  to  every  part  of  the  myocardium. 

The  valves  of  the  heart  are  formed  of  folds  of  endocardium 
strengthened  by  fibrous  tissue  (fig.  303,  C).  This  tissue  forms  a  thicken- 
ing near  the  free  edge  of  the  valve  (c).  At  the  base  of  the  auriculo- 
ventricular  valves  the  muscular  tissue  of  the  auricle  may  be  found 
passing  a  short  distance  into  the  valve.  In  the  foetus  these  valves  are 
at  first  entirely  muscular. 

The  nerves  of  the  heart  are  seen  in  sections  underneath  the  epi- 
cardium  of  both  auricles  and  ventricles  ;  in  the  former  situation  they 
are  connected  at  intervals  with  small  ganglia  (fig.  303,  A,  g].  Their 
branches  pass  to  the  muscular  substance,  and  after  dividing  into  fine 
fibrils,  these  end  in  enlarged  extremities,  which  are  applied  directly  to 
the  muscular  fibres  (Ranvier).  Other  nerve-fibres,  which  are  probably 
afferent,  terminate  in  complex  ramifications  in  the  endocardium  in 
connection  with  small  masses  of  nucleated  cells,  forming  a  kind  of  end- 
plate  (Smirnow). 

The  blood-vessels  of  the  heart  are  very  numerous,  and  the  veins  thin- 
walled,  retaining  the  capillary  structure  (endothelium  only)  in  vessels 
of  as  much  as  0-25  mm.  in  diameter.  They  are  accompanied  by 
numerous  lymphatic  vessels,  which  also  form  plexuses  under  the  cardiac 
pericardium  and  endocardium.  The  lymphatics  appear  to  be  in  free 
communication  with  the  spaces  of  the  interstitial  connective  tissue 
between  the  muscle-fibres. 


I 


254  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    XXVII. 
THE   TRACHEA   AND  LUNGS. 

1.  In  sections  of  the  trachea  and  larynx,  notice  the  epithelium,  the  basement- 
membrane  (of  some  thickness  in  the  human  trachea),  the  lymphoid  tissue  of 
the  mucous  membrane,  the  elastic  tissue  external  to  this,  and,  lastly,  the 
fibrous  membrane  containing  the  cartilages.  In  the  mucous  membrane  and 
submucous  areolar  tissue  look  for  sections  of  mucous  glands,  ducts  of  which 
may  be  seen  opening  on  the  surface.  At  the  back  of  the  trachea  notice  the 
plain  muscular  fibres  transversely  arranged  ;  there  may  be  larger  mucous 
glands  external  to  these. 

2.  In  sections  of  lung  notice  the  sections  of  the  alveoli  collected  into  groups 
(air-sacs).  Find  sections  of  bronchial  tubes,  some  cut  longitudinally  and 
passing  at  their  extremities  into  the  alveolar  passages,  others  cut  across.  In 
each  tube  notice  the  ciliated  epithelium  internally.  Next  to  this  the  mucous 
membrane  containing  numerous  elastic  fibres  and  often  thrown  into  folds  ; 
then  the  layer  of  circular  muscular  fibres,  and,  outside  this,  loose  fibrous 
tissue  in  which  in  larger  bronchial  tubes  pieces  of  cartilage  may  be  seen 
embedded.  Small  mucous  glands  may  also  be  obsei'ved  in  the  fibrous  tissue 
sending  their  ducts  through  the  other  layers  to  open  on  the  inner  surface. 
Notice  that  the  section  of  a  branch  of  the  pulmonary  artery  always  accom- 
panies a  section  of  a  bronchial  tube. 

In  the  sections  of  the  alveoli  observe  the  capillary  vessels  passing  from  one 
side  to  the  other  of  the  intervening  septa ;  and  in  places  where  the  thin  wall 
of  an  alveolus  is  to  be  seen  in  the  section,  the  network  of  blood-capillaries 
upon  it.  Notice  within  the  alveoli  nucleated  corpuscles  which  frequently 
contain  dark  particles  in  their  protoplasm.  They  are  amoeboid  cells  which 
have  migrated  from  the  blood-vessels  and  lymphatics,  and  have  taken  in 
inhaled  particles  of  carbon.  They  may  pass  back  into  the  lung  tissue,  for 
similar  cells  are  seen  in  this.  Make  a  sketch  of  part  of  the  wall  of  one 
or  more  bronchial  tubes  and  of  one  or  two  of  the  alveoli.  ;, 

3.  In  sections  of  a  fresh  lung  the  air-cells  of  which  have  been  filled  with  a 
mixture  of  gelatine  and  nitrate  of  silver  solution,  the  epithelium  of  the  alveoli 
may  be  studied.  The  sections  can  be  made  with  the  freezing  microtome,  and 
mounted  in  glycerine,  which  should  be  warmed  after  the  cover-glass  is  applied 
in  order  to  melt  the  gelatine. 

4.  Mount  a  section  of  lung  in  which  the  pulmonary  vessels  have  been 
injected.  Study  the  general  arrangement  of  the  vessels  with  a  low  power, 
and  the  network  of  capillaries  of  the  alveoli  with  a  high  power.  Observe 
that  the  veins  run  apart  from  the  arteries.  Sketch  the  capillary  netwoi'k  of 
one  or  two  adjoining  alveoli. 


The  Trachea. 


The  trachea  or  windpipe  is  a  fibrous  and  muscular  tube,  the  wall 
of  which  is  rendered  somewhat  rigid  by  C-^haped  hoops  of  cartilage 


thp:  tracihea  and  lungs. 


255 


which  are  embedded  in  the  fibrous  tissue.  The  muscuhir  tissue,  which 
is  of  the  plain  variety,  forms  a  flat  band,  the  fibres  of  which  run  trans- 
versely at  the  back  of  the  tube.  The  trachea  is  lined  by  a  mucous 
membrane  (fig.  305,  a  to  d),  which  has  ciliated  epithelium  upon  its 
inner  surface.  The  epithelium-cells,  which  have  been  already  described 
(Lesson  VIII.),  rest  upon  a  thick  basement-membrane.     The  corium  of 


0^ 


'i0 


1^<S>, 


^« 


a^s^i»#io 


^MMoWWMm%i 


'90% 


Fig.  305.— Longitudinal  section  of  the  human  trachea,  including  portions 
OF  TWO  CARTILAGINOUS  RINGS.     (Klein.)     Moderately  magnified. 

a,  ciliated  epithelium  ;  6,  basement-membrane;  c,  superficial  part  of  the  mucous  mem- 
brane, containing  the  sections  of  numerous  capillary  blood-vessels  and  much 
lymphoid  tissue ;  d,  deeper  part  of  the  mucous  membrane,  consisting  mainly  of 
elastic  fibres;  f,  submucous  areolar  tissue,  containing  the  larger  bIood-ves.sels,  small 
mucous  glands  (their  ducts  and  alveoli  are  seen  in  section),  fat,  etc.  ;  /',  fibrous  tissue 
investing  and  uniting  the  cartilages  ;  g,  a  small  mass  of  adipose  tissue  in  the  fibrous 
layer ;  h,  cartilage. 


the  mucous  membrane  consists  of  areolar  and  lymphoid  tissue,  and 
contains  numerous  blood-vessels  and  lymphatics.  In  its  deepest  part 
is  a  well-marked  layer  of  longitudinal  elastic  fibres  {d).  Many  small 
glands — mucous  and  mixed  mucous  and  serous — are  found  in  the  wall 
of  the  trachea.  They  may  lie  either  within  the  mucous  membrane  or 
in  the  submucous  areolar  tissue  {e)  or,  lastly,  at  the  back  of  the 
trachea,  outside  the  transverse  muscular  fibres. 

The  two  divisions  of  the  trachea,  the  hronchi,  are  precisely  similar  in 
structure  to  the  main  tube. 


256  THE   ESSENTIALS   UF   HIST(jLOGY. 

The  larynx  is  also  very  like  the  trachea  so  far  as  the  structure  of 
the  mucous  membrane  is  concerned.  It  is  lined  by  ciliated  epithelium, 
but  over  the  true  vocal  cords  and  upon  the  epiglottis,  as  well  as  here 
and  there  in  the  part  above  the  glottis,  stratified  epithelium  is  found  : 
and  taste-buds  may  occur  in  this  epithelium,  except  over  the  vocal 
cords.  The  nerve-endings  in  the  epithelium  are  shown  in  fig.  218, 
p.  176. 

The  lymphoid  tissue  is  especially  abundant  in  the  mucous  membrane 
of  the  ventricle  of  Morgagni  (fig.  306,  d).  and  a  large  number  of  mucous 
glands  open  into  this  ca'vity  and  into  that  of  the  sacculus. 


^^  -  ■ 


1 


\  '--'-'.^ 


d 


f^ 


Fig.  306.  — LoxGrrcDHfAL  SEcnox  theocgh  the  ve>teicle  of  the  laeyxx 

OF  A  CHILD.     (Klein.) 

a,  true  vocal  cord  ;  6,  false  vocal  cord ;  c,  nodule  of  cartilage  ;  d,  ventricle  of  Morgagni ; 

I,  lymphoid  tissue ;  m,  thyro-arytenoid  muscle. 

The  true  vocal  cords  are  composed  of  fine  elastic  fibres. 

The  cartilages  of  the  trachea  and  the  thyroid,  cricoid  and  arytenoid 
cartilages  of  the  larynx  are  hyaline ;  all  these  are  liable  to  ossify  as 
age  advances.  The  epiglottis  and  the  cartilages  of  Santorini  and  of 
Wrisberg  are  composed  of  elastic  fibro-cartilage.  This  is  also 
the  case  with  the  uppermost  part  of  the  arytenoid  and  the  tip  of  the 
vocal  process. 

The  Lungs. 

The  lungs  are  formed  by  the  ramifications  of  the  hronchicd  tubes  and 
their  terminal  expansions,  which  form  groups  or  lobules  of  sacculated 


THE   LUNGS. 


257 


dilatations  (air-sacs,  infundibula),  beset  everywhere  with  small  irregu- 
larly hemispherical  or  cubical  bulgings,  kno^\^l  as  the  air-cells  or 
pulmonart/  alveoli. 

The   bronchial   tubes   (tigs.   307,    308,   309)   are  lined  (except   the 


Fig.  307. — Portion"  of  a  traxsverse  section  of  a  broxchial  tube,  hum  ax, 
6  MM.  IX  diameter.     (F.  E.  Schultze. )    Magnified  30  diameters. 

a,  cartilage  and  fibrous  layer  with  mucous  glands,  and,  in  the  outer  part,  a  little  fat ; 
in  the  middle,  the  duct  of  a  gland  opens  on  the  inner  surface  of  the  tube ;  h, 
annular  layer  of  involuntary  muscular  fibres  ;  c,  elastic  layer,  the  elastic  fibres  in 
bundles  which  are  seen  cut  across ;   d,  columnar  ciliated  epithelium. 


-^r-^^. 


Fig.  308. — Section  op  part  of  a  bronchial  tube.     Magnified  200  diameters. 

a,  ciliated  epithelium  ;  6,  basement  membrane  ;  c,  superficial  part  of  mucous  membrane, 
with  fine  elastic  fibres  ;  d,  deeper  part  with  numerous  coarser  fibres  ;  e,  plain  muscle 
of  bronchus  ;  /,  duct  of  gland  passing  through  mucous  membrane. 

R 


258 


THE   ESSENTIALS  OF  HISTOLOGY. 


terminal  bronchi)  by  ciliated  epithelium  which  rests  on  a  basement- 
membrane.  External  to  this  is  the  corium  of  the  mucous  membrane, 
containing   a   larsje   number   of  longitudinal   elastic  fibres    and    some 


Fig.  309.- 


-Section  of  a  small  bronchial  tube,  human.     (Sobotta.) 
The  elastic  fibres  of  the  mucous  membrane  are  stained. 


x280. 


Fig.  310.— Cast  of  lobule  of  dog's  lung  showing  a  single  infundibuluji 

OR  AIR-SAC.     (W.  S.  Miller). 
A,  atrium;    r,  vestibule  or  alveolar  duct  leading  to  atrium  (seen  in  section);  8,  air-sac 
(infundibulum) ;  P,  section  of  the  neck  of  a  second  air-sac  (cut  away).     The  irregular 
projections  on  the  atrium  and  air-sac  are  the  alveoli. 

lymphoid  tissue.  Outside  this  again  is  a  complete  layer  of  plain 
muscular  fibres  encircling  the  tube.  Next  comes  a  loose  fibrous  layer 
in  which,  in  the  larger  tubes  (fig.  307),  small  plates  of  cartilage 
are  embedded.     Mucous  glands  are  also  present  in  this  tissue. 


THE   LUNGS. 


259 


The  extremities  of  the  bronchial  tubes  expand  into  passages,  the 
respiratory  bronchioles,  which  give  off  branches,  termed  alveolar  duds  or 
terminal  bronchioles.  The  walls  of  these  are  beset  with  alveoli.  The 
terminal  bronchioles  lead  through  nearly  spherical  alveolated  dilata- 
tions (the   atria)  into   a   number   of  blind   and   often   funnel-shaped 


-Section  of  cat's  lung,  outlined  with  camera  lucida. 
(W.  S.  Miller.) 
The   shading  indicates  the  position   of  plain   muscular   tissue.     V,  pulmonary   veins  ; 
A,  atria  ;  A.  S,  air-sacs  ;  T.  B,  terminal  bronchioles  or  alveolar  ducts ;  B.  R,  respira- 
tory bronchioles ;  B,  small  bronchus. 

diverticula  completely  covered  with  alveoli ;  these  are  known  as  the 
infunclibula,  alveolar  sacs  or  air-sacs  (Waters).  The  arrangement  of 
these  parts,  according  to  the  investigations  of  AV.  S.  Miller,  is  as 
follows : — Two  or  more  air-sacs,  or  groups  of  alveoli,  open  into  a 
common  chamber  (atrium),  and  three  to  six  atria  into  an  alveolar  duct 
or  tcrrnincd  bronchiole.  The  latter  open  into  the  respiratory  bronchioles, 
which  are  expanded  continuations  of  the  smallest  bronchi.  All  of 
these,  except  the  last  named,  are  beset  with  alveoli. 

The  epithelium  changes  in  character  in  the  alveolar  ducts ;   from 


260 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fig.  312.— Diagram  of  the  ending  of  a  bronchial  tube.  (W.  S.  Miller.) 

B,  terminal  bronchiole  ;  V,  vestibule  ;  A,  atrium  ;  S,  air-sac  (inf  undibuluni) ;  C,  air-cell 
(alveolus) ;  P,  ending  of  pulmonary  arteriole ;  T,  commencement  of  pulmonary 
venule. 


Fig.  313.  — Section  of  part  of  cat's  lung,  stained  with  nitrate  of  silver. 
(Klein.)     Highly  magnified. 

Both  the  cubical  and  the  large  flattened  cells  of  the  alveoli  are  shown.  In  the  middle 
is  a  section  of  a  lobular  bronchial  tube,  with  a  patch  of  cubical  epithelium  cells 
at  one  side. 


THE   LUNGS.  261 

columnar  and  ciliated  it  becomes  cubical  and  non-ciliated,  and  there 
are  patches  of  the  respiratory  epithelium  (see  below)  not  only  in  the 
alveoli  which  beset  the  ducts,  but  also  elsewhere  in  their  wall.  The 
plain  muscular  tissue  of  the  bronchiole  is  continued  on  the  walls  of 
the  alveolar  ducts,  but  not  on  those  of  the  atria,  although  some 
occurs  round  the  mouths  of  the  atria  and  even  of  the  alveoli. 

The  alveoli  are  lined  by  large  irregular  flattened  cells  (fig.  313), 
which  form  an  extremely  delicate  layer  (respiratory  epithelium), 
separating  the  blood-capillaries  from  the  air  within  the  alveoli. 
Amongst  the  flattened  cells  are  here  and  there  groups  of  smaller  and 
thicker  (cubical)  epithelium-cells.     The  capillary  network  of  the  alveoli 


Fig.  314. — Section  of  injected  lung  of  kabbit.  including  several  con- 
tiguous ALVEOLI.     (Szymonowicz. )     Magnified  300  diameters. 

is  very  close  (fig.  314),  and  the  capillary  vessels  of  adjoining  alveoli  are 
in  complete  continuity,  the  vessels  passing  first  to  one  side  and  then 
to  the  other  of  the  septa  which  separate  the  adjacent  alveoli.  Outside 
the  epithelium  a  thin  layer  of  connective  tissue  (basement  membrane  1) 
forms  the  wall  of  each  alveolus.  Elastic  fibres  are  numerous  around 
the  mouths  of  the  alveoli,  and  a  certain  number  course  over  the  wall 
of  each  alveolus. 

Blood-vessels. — Branches  of  the  pulmonary  artery  accompany  the 
bronchial  tubes  to  be  distributed  to  the  capillary  networks  upon  the 
alveoli,  from  which  the  blood  is  returned  by  the  pulmonary  veins. 
An  arteriole  runs  with  each  terminal  bronchiole,  and,  dividing  into  as 
many  branches  as  there  are  atria,  is  distributed  to  the  capillary  net- 
works  of  all   the   air-cells  with  which   the   bronchiole   is   connected 


262  THE   ESSENTIALS   OF   HISTOLOGY. 

(Miller).  From  these  networks  one  or  two  venules  collect  the  blood, 
usually  coursing  (independently  of  the  arteriole)  on  the  outer  border 
of  the  group  of  infundibula,  and  unite  with  other  venules  to  form 
efferent  veins.  The  venules  of  the  superficial  lobules  are  connected 
with  a  vascular  network  at  the  surface  of  the  lung  underneath  the 
pleura.  The  veins,  pursuing  a  separate  course  through  the  tissue  of 
the  lung,  join  with  others  to  form  larger  vessels  which  pass  to  the 
root  of  the  lung.  Branches  from  the  bronchial  arteries  are  distributed 
to  the  walls  of  the  bronchial  tubes,  and  to  the  connective  tissue  of  the 
lung.  Bronchial  veins  accompany  the  bronchial  arteries  to  the  larger 
tubes,  but  most  of  the  blood  brought  to  the  lungs  by  the  bronchial 
arteries  is  returned  by  the  pulmonary  veins.  Connective  tissue 
intervenes  everywhere  in  small  quantity  between  the  infundibula 
(interstitial  tissue),  and  forms  a  distinct  layer,  containing  much 
elastic  tissue,  covering  the  surface  of  the  lung  underneath  the  serous 
membrane  (subserous  tissue).  In  some  animals  {e.g.  guinea-pig)  the 
subserous  layer  contains  plain  muscular  tissue,  which  is  especially 
developed  near  the  lung-apex ;   it  has  not  been  detected  in  man. 

The  lymphatics  of  the  lung  accompany  the  bronchial  tubes,  the 
branches  of  the  pulmonary  artery,  and  the  branches  of  the  pulmonary 
vein ;  and  they  also  form  a  network  in  the  pleura.  The  atria  and 
air-sacs  have  no  lymphatics  in  their  walls  (Miller).  The  bronchial 
lymphatics  are  less  superficial  than  the  corresponding  blood-vessels. 
The  larger  tubes  have  two  plexuses,  one  within  the  other  outside  the 
cartilages.  The  smaller  have  only  one  set.  The  lymphatics  of  the 
bronchi  are  connected  with  those  of  the  arteries  and  veins  by  lateral 
branches  curving  off  at  the  divarications  of  the  tubes  ;  at  these  points 
there  is  usvxally  an  accumulation  of  lymphoid  tissue.  The  larger 
arteries  and  veins  have  two  accompanying  lvm})hatics,  the  smaller  only 
one.  All  the  lymphatics  tend  towards  the  hilus,  and  enter  lymphatic 
glands  at  the  root  of  the  lung.  Those  in  the  pleura  have  been  said  to 
communicate,  by  means  of  stomata  between  the  epithelial  cells  of  the 
serous  membrane,  with  the  cavity  of  the  pleura,  but  this  connexion  is 
denied  by  Miller.  The  lymphatics  of  the  pleura  are  furnished  with 
numerous  valves. 

The  pleura,  which  covers  the  surface  of  the  lung,  has  the  usual 
structure  of  a  serous  membrane.  It  is  provided  with  a  special  net- 
work of  blood-vessels,  which  is  supplied  from  the  pulmonary  vessels  of 
the  superficial  lobules. 


THE   TEETH.  263 


LESSOX    XXYIII. 
STRUCTURE  AND  DEVELOPMEST  OF  THE  TEETH. 

1.  Study  first  with  the  low  power  and  afterwards  with  the  high  power  a 
longitudinal  section  of  a  human  tooth  which  has  been  prepared  by  grinding. 
It  is  better  to  purchase  this  specimen,  for  the  process  of  preparation  is 
difficult  and  tedious  without  the  aid  of  special  apparatus.  Examine  care- 
fully the  enamel,  the  dentine,  and  the  cement.  The  dark  appearance  of  the 
dentinal  tubules  is  due  to  their  containing  air  in  the  dried  specimen. 
Measure  the  diameter  of  the  enamel  prisms  and  of  some  of  the  dentinal 
tubules.     Make  sketches  from  each  of  the  tissues. 

2.  Section  of  a  tooth  in  situ,  which  has  been  decalcified  after  fixation,  and 
stained.  In  this  section  the  mode  of  implantation  of  a  tooth,  as  well  as  the 
structure  of  the  pulp,  can  be  made  out.  Make  a  genei'al  sketch  under  a  low 
power,  and  under  a  high  power  draw  a  small  piece  of  the  pulp  showing  the 
processes  of  the  odontoblasts  extending  into  the  dentinal  tubules. 

3.  The  development  of  the  teeth  and  the  formation  of  their  tissues  are 
studied  in  sections  made  across  the  snout  and  lower  jaw  of  fcetal  and  young 
animals.  The  preparations  may  be  stained  in  bulk  or  the  individual  sections 
mav  be  stained. 


The  Teeth. 

A  tooth  consists  in  man  of  three  calcified  tissues ;  the  enamel,  which 
is  of  epithelial  origin,  the  dentine,  and  the  cement  or  cruda  jiefrosa. 
The  dentine  forms  the  main  substance  of  a  tooth,  the  enamel  covers 
the  crowni,  and  the  cement  is  a  layer  of  bone  which  invests  the  root 
(figs.  315  to  317). 

Enamel  is  formed  of  elongated  hexagonal  jmsms  (figs.  318,  319), 
which  are  set  vertically,  or  with  a  slight  curvature,  upon  the  surface 
of  the  dentine.  They  are  marked  at  tolerably  regular  intervals  with 
slight  transverse  shadings  producing  an  indistinct  cross-striated  appear- 
ance. Sometimes  coloured  lines  run  through  the  enamel  across  the 
direction  of  its  prisms.  The  enamel  prisms  have  when  first  laid  down 
a  fibrous  structure,  but  this  becomes  obscured  after  their  calcification 
is  complete.  C.  Tomes  has  shown  that  the  enamel  of  the  fully-formed 
tooth  contains  only  an  extremely  minute  proportion  of  animal  matter  : 
practically  it  is  wholly  composed  of  earthy  matter  (lime  salts). 

Dentine  is  constituted  of  a  hard  dense  substance  like  bone,  but 
containing  no  Haversian  canals  or  lacunae.  It  is  pierced  everywhere 
by  fine  canaliculi  {dentinal  tubules,  fig.  320),  radiating  outwards  from  a 


264 


THE   ESSENTIALS   OF   HISTOLOGY. 


central  cavity  which,  during  life,  contains  the  pulp.  The  tubules  branch 
at  acute  angles  as  they  pass  outwards  ;  their  branches  become  gradually 
finer  towards  the  periphery  of  the  dentine.  The  dentinal  tubules  are 
occupied  by  processes  of  the  odontoblasts  (p.  268). 


Fig.  315. — Vertical  section  of  a  tooth  in  situ.     (Waldeyer. ) 
c,  is  placed  in   the   pulp-cavitj^,   opposite  the   cervix  or  neck  of   the  tooth  ;   the  part 
above  is    the   crown,    that  below  is   the  root  (fang).     1,  enamel  with  radial  and 
concentric  markings  ;   £'',  dentine  with  tubules  and  incremental  lines  ;    3,  cement 
or  crusta  petrosa,  with  bone  corpuscles  ;  I,,  dental  j^eriosteum  ;  ;',  bone  of  lower  jaw. 

The  tubules  have  a  proper  wall  of  their  own,  which  can  be  isolated 
by  steeping  a  section  of  tooth  in  strong  hydrochloric  acid.  In  the 
living  tooth  they  are  occupied  by  protoplasmic  fibres  (Tomes'  fibres), 
which  are  prolonged  from  the  superficial  cells  of  the  pulp. 

The  intertubular  substance  appears  for  the  most  part  homogeneous, 


THE   TEETH. 


265 


but  here  and  there  indications  can  be  seen  in  it  of  a  globular  forma- 
tion. This  is  especially  the  case  near  the  surface  of  the  dentine, 
where  tiie  globular  deposit  and  the  interglobular  spaces  may  produce 


X^^N.. 


/ 


A  '^' 


\      1 


//    D 


Fig.  316.— Section  of  molar  tooth.     (Sobotta.)     x8. 
E,  enamel ;  D,  dentine ;  C,  cement ;  P,  pulp  cavity. 


266 


THE   ESSENTIALS   OF   HISTOLOGY. 


a  granular  appearance  {granular  layer,  fig.  317,  g),  and  also  in  the 
course  of  certain  lines  or  clefts  which  are  seen  traversing  the  dentine 
across  the  direction  of  the  tubules  {inter glohular  spaces,  incremental  lines, 


Fig.  317.— Cross-sectiox  of  root  of  canine  tooth,  human. 

(Sobotta. )      X  2.5. 

D,  dentine  ;  G,  its  granular  layer  ;  C,  cement ;  P,  pulp  cavity. 


fig.    31.5,   shown   magnified    in    fig.    322).      After   decalcification   the 
dentine  can  be  separated  into  lamellae  along  these  incremental  lines. 

The  animal  matter  of  dentine  resembles  bone  and  the  connective 
tissues  generally  in  having  its  ground-substance  pervaded  by  fibres 
which   yield    gelatine    on    boiling.      These    fibres,    which    have   been 


THE   TEETH. 


267 


especially  investigated  by  v.  Ebner  and  by  Mummery,  are  difficult  of 
demonstration  in  the  fully  calcified  dentine;  but  in  developing 
dentine  and  in  tlentine  which  is  attacked  by  caries  they  are  more 
easily  shown. 


'-'r!i::Hi.l|/|.|:j-p'   /,  ())  Vil.l\         ,      ,  ■ 


mmiii:. 


■I 


W^''^' 


Fig.  318.— Section  through  the  e.vamkl  op  a  tooth.     Magnified  200 
diameters.     (Rauber.) 

a,  projection  of  dentine,  showing  some  of  its  tubules,  b,  penetrating  into  the 
enamel;  c,c,  enamel  fibres  cut  longitudinally;  d,  d,  prisms  cut  transversely 
e,  cuticle  of  the  enamel.  •'  ' 


Fig.  319.— Examel  prisms.     Magnified  350  diameters.     (Kolliker.) 
A,  Fragments  and  single  fibres  of  the  enamel,  isolated  by  the  action  of  hydrochloric  acid. 
a,  surtace  of  a  smaU  fragment  of  enamel,  showing  the  hexagonal  ends  of  the  fibres. 


268 


THE   ESSENTIALS   OF  HISTOLOGY. 


The  pulp  (fig.  323)  consists  of  a  soft,  somewhat  jelly-like,  connective 
tissue,  containing  many  branched  cells,  a  network  of  blood-vessels,  and 
many  nerve-fibres  which  pass  into  the  pulp-cavity  along  with  the  blood- 
vessels by  a  minute  canal  at  the  apex  of  the  fang.     The  superficial 


Fig.  321. 


Fig.  320. 


Fig.  322. 


Fig.  320.~Section  of  fang,  pae.\llel  to  the  dentinal  tubules.     Magnified 

300  diameters.     (Waldeyer. ) 

1,  cement,  with  large  bone  lacunas  and  indications  of  lamellas;   2,  granular  layer  of 

Purkinje  (interglobular  spaces)  ;  3,  dentinal  tubules. 

Fig.  321. — Sections  of  dentinal  tubules.     Magnified  about  300  diameters. 

(Fraenckel.) 
ft,  cut  across  ;  b,  cut  obliquely. 

Fig.    322. — A    small   portion    of    dentine   with    interglobular    spaces. 

Magnified  350  diameters.     (KoUiker.) 

c,  portion  of  incremental  line  formed  by  the  interglobular  spaces,  which  are  here  filled 

up  by  a  transparent  material. 


cells  of  the  pulp  form  an  almost  continuous  layer,  like  an  epithelium 
(fig.  323,  Od,  OcV).  They  are  known  as  odontohlasts,  from  having  been 
concerned  in  the  formation  of  the  dentine.  The  nerve-fibres  are  said 
to  pass  eventually  between  the  odontoblasts  and  to  end  in  arborisa- 


THE   TEETH. 


269 


tions  close  to  the  dentine,  but  they  have  not  been  followed  into  the 
dentinal  tubules. 

The  crusta  petrosa  (fig.  317,  320)  is  a  layer  of  laraellated  bone, 
including  lacunie  and  canaliculi,  but  without  Haversian  canals,  at  least 
normally,  in  the  human  teeth.  It  is  covered  with  periosteum  (dental 
periiisfeum),  which  also  lines  the  socket,  and  serves  to  fix  the  tooth 
securely. 


Od' 


Fig.  .323.— Section  across  the  eoot  of  a  youxg  tooth  showixg  the  pulp 
IN  siTC.     (Rose.) 

P,  pulp ;  V,  V,  veins  ;  A,  A,  A,  arterioles  ;  N,  nerve  bundles  ;  O'l,  columnar  odontoblasts 
still  depositing  dentine  ;  Od',  flattened  odontoblasts  which  have  ceased  to  form 
dentine. 


Formation  of  the  teeth. — The  teeth  are  developed  somewhat  similarly 
to  the  hairs.  A  continuous  thickening  of  the  epithelium  occurs  along  the 
line  of  the  gums,  and  grows  into  the  corium  of  the  mucous  membrane 
{common  dented  germ  or  (hnfal  lamina,  fig.  32-1:,  a).  At  regular  intervals 
there  is  yet  a  further  thickening  and  growth  from  the  common  germ 
into  the  tissue  of  the  mucous  membrane,  each  of  these  special  rudi- 
ments, which  are  ten  in  number,  swelling  out  below  into  a  flask-shaped 
mass  of  cells,  the  special  dental  germ  (fig.  324,  b)  of  a  milk  tooth.  The 
intermediate  parts  of  the  dental  lamina  long  remain,  forming  a  common 
epithelial  strand  uniting  the  several  special  dental  germs  to  one  another 
and  to  the  epithelium  covering  the  gum  (fig.  324,  C,  D,/).  A  vascular 
papilla  is  continued  from  the  corium  into  the  bottom  of  each  special 


270 


THE   ESSENTIALS   OF   HISTOLOGY. 


germ  (fig.  324,  C,  D,  p)  :  this  papilla  has  the  shape  of  the  crown  of  the 
future  tooth.     Each  special  dental  germ,  with  its   included   papilla, 

B 
A 

6- 

/ 


:WM^^ 


d'Y 


■H 


c  f 


f:im0& 


Fig.  324. 


A.  SECTIOX  ACBOSS  the   CPPEB  jaw  of  a   FCETAL  sheep,    .3  CENTIMETERS  LONG. 

(Waldeyer. ) 
1,  common  dental  lamina  dipping  down  into  the  mucous  membrane  where  it  is  half  sur- 
rounded hy  a  horsc-hoe-shaped  more  den.se-looking  tissue,  the  germ  of  the  dentine 
and  dental  sac  ;  2,  palatine  process  of  the  maxilla. 

B.  Section'  from  fcetal  calf  similar  to  that  shown  in  A,  but  passing  through 

ONE  OF  THE  SPECIAL  DENTAL  GERMS  HERE  BECOMING  FLASK-SHAPED.       (Rose. ) 

a,  epithelium  of  mouth,  thickened  at  b,  above  special  dental  germ  ;  c,  papilla ;  d,  special 

dental  germ  ;  -:,  enamel  epithelium  ;  /",  dental  sac. 

C  AND  D.  Sections  at  lateb  stages  than  A  and  B,  the  papilla  having 

BECOME      FORMED      AND      HAVING      BECOME      PARTLY      SURROUNDED     BY     THE 

EPITHELI.\L  GERM.     (Kolliker. ) 
c,  epithelium  of  gum,  sketched  in  outline ;  /,  neck  of  dental  germ ;  f,  enamel  organ  ;  e, 
its  deeper  columnar  cells  ;  e',  projections  into  the  corium  ;  p,  papilla  ;  j*,  dental  sac 
forming.     In  D,  the  dental  germ  (jp)  of  the  corresponding  permanent  tooth  is  seen. 


FORMATION   OF  THE   TEETH.  271 

presently  becomes  almost  entirely  cut  ofl"  from  the  epithelium  of  the 
mouth,  and  surrounded  by  a  vascular  membrane — the  dental  sac. 
The  papilla  becomes  transformed  into  the  dentine  and  pulp  of  the 
future  tooth,  and  the  enamel  is  deposited  upon  its  surfece  by  the 
epithelial  cells  of  the  dental  germ.  The  root  of  the  tooth,  with  its 
covering  of  cement,  is  formed  at  a  later  period,  when  the  tooth  is 
beginning  to  groAv  up  through  the  gum,  by  a  gradual  elongation  of  the 
base  of  the  papilla.     The  shaping  of  this  into  the  form  of  the  root  is 


wl 


e" 


UK 


<sv 


VK 


Fig.  32.5.— Section  of  a  developing  incisor  tooth  of  a  human  embkto. 
(Rose.)    The  section  also  includes  the  germ  of  the  adjacent  tooth. 

DK,  dental  i)apilla ;  od,  odontoblasts ;  6,  bone  of  jaw ;  e,  e',  outer  and  inner  layers  of 
enaiuel-organ  ;  S.P.,  enamel  pulp;  d.f.  dental  furrow;  c,  reriialns  of  common  dental 
germ  or  lamina ;  n,  neck  or  bridge  of  cells  connecting  this  with  the  enamel-organ  ; 
vi.e.,  mouth-epithelium;  e",  enamel  organ  of  adjacent  tooth-germ;  /•,  reserve  germ 
of  permanent  tooth. 

determined  by  a  growth  of  the  epithelium  of  the  edge  of  the  enamel 
germ,  which  extends  in  the  form  of  a  fold  (the  epithelial  sheath  of 
V.  Brunn)  towards  the  future  apex  of  each  fang. 

Previously  to  the  deposition  of  the  enamel,  the  dental  germ  under- 
goes a  peculiar  transformation  of  its  previously  polyhedral  epithelium- 
cells  into  three  layers  of  modified  cells.  One  of  these  is  a  layer  of 
columnar  cells  {ameloblasfs,  fig.  326,  a),  immediately  covering  the  surface 
of  the  dentine.  The  enamel-prisms  are  produced  by  a  fibrous  forma- 
tion (fig.  327,  /)  followed  by  a  deposition  of  calcareous  salts  ;  these 
changes  taking  place  altogether  external  to  the  cells  (or,  as  some  hold, 
by  a  direct  calcification  of  their  protoplasm).  The  cells  next  to  the 
dental  sac  form  a  single  layer  of  cubical  epithelium  (fig.  325,  e),  and 


272 


THE   ESSENTIALS   OF  HISTOLOGY. 


nearly  all  the  other  cells  of  the  dental  germ  become  transformed  into 
branching  corpuscles  (fig.  325,  SP ;  fig.  326,  ;j)  communicating  by 
their  processes,  and  thus  forming  a  continuous  network.  The  dental 
germ,  after  it  is  thus  modified,  is  known  as  the  enamel  organ. 

The  (h'nfine  of  the  tooth  is  formed  by  calcification  of  the  surface  of 
the  papilla.  At  this  surface  there  is  a  well-marked  layer  of  odonto- 
blasts (fig.  328,  od,  fig.  329,  c),  and  these  produce  a  layer  of  dentinal 
matrix  which  forms  a  sort  of  cap  to    the   papilla,    and    which  soon 


'^'/sy-' 


.-ISv- 


~3     *t^. 


^« 


W.u^^i 


Fig.  327. 


Fig.   326.— Section  shovvixg  the  structure  of  the  part  of  the  enamel 

ORGAN  WHICH  LIES  NEXT  TO  THE  DENTINE.       (Rose.) 

d,  dentine ;  o,  newly  formed  enamel  stained  black  by  osmic  acid  ;  T,  Tomes'  processes 
from  the  ameloblasts,  a;  str.  int.,  stratum  intermedium  of  enamel-organ;  p, 
branched  cells  of  enamel  pulp. 

Fig.  327. — Developing  enamel  showing  ameloblasts  and  the  fibrous  sub- 
stance    PRODUCED     BY     THESE     CELLS,     WHICH    FORMS    THE     BASIS    OF     THE 

ENAMEL  PRISMS.     (From  a  photograph  by  Leon  Williams.) 
a,  portions  of  the  ameloblasts  ;  /,  fibrous  basis  of  enamel  jirisms  ;  e,  calcified  part  of  enamel. 


becomes  calcified  by  the  deposition  of  globules  of  calcareous  matter. 
Processes  of  the  odontoblasts  remain  in  the  dentine  as  it  is  forming, 
and  thus  the  dentinal  tubules  are  produced.  Subsequently  other  layers 
of  dentine  are  formed  within  the  first  by  a  repetition  of  the  same 
process,  and  in  this  way  the  papilla  gradually  becomes  calcified.  A 
part,  however,  remains  unaltered  in  the  centre  of  the  tooth,  and  with 
its  covering  of  odontoblasts  forms  the  pulp. 

The  ten  milk-teeth  are  formed  in  each  jaw  in  the  manner  described. 
These,  however,  become  lost  within  a  few  years  after  birth,  and  are 
replaced  by  permanent  teeth  in  much  the  same  way  that  a  new  succes- 
sion of  hair  occurs.     A  small  outgrowth  takes  place  at  an  early  period 


FORMATION   OF  THE  TEETH. 


273 


from  the  dentul  germ  close  to  each  of  the  milk-teeth  (fig.  324,  D,  fp), 
and  this  eventually  becomes  the  germ  of  the  corresponding  permanent 
tooth       It  gradually   enlarges,   acquires  a   papilla,   forms  an    enamel 


Fig.  328. — Section  op  part  of  a  developing  tooth.     (From  a  photograph  by 

Leon  Williams.) 
d,  dentine ;    od,   odontoblast-s   sending  their  processes  into  the   dentinal   tubules  ;   p, 

branched  cells  of  the  pulp  ;   f ,  developing  enamel ;   a,  ameloblasts  ;   r,  reticulum  or 

spongework  of  the  enamel  organ. 


Fig.  329. — Part  of  section  of  developing  tooth  of  young   rat,  showing 

THE  mode  of  deposition  OF  THE  DENTINE.      Highly  magnified. 

a,  outer  layer  of  fully  calcified  dentine;  6,  uncalcified  matrix,  with  a  few  nodules  of 

calcareous  matter ;  c,  odontoblasts  with  processes  extending  into  the  dentine  ;  d, 

pulp.     The  section  being  stained,  the  uncalcified  matrix  is  coloured,  but  not   the 
calcified  part. 

s 


274  THE   ESSENTIALS   OF   HISTOLOGY. 

organ  :  in  short,  passes  through  the  same  phases  of  development  as 
the  germ  of  the  milk-tooth  ;  and  when  the  milk-tooth  drops  out  of  the 
jaw  in  consequence  of  the  absorption  of  its  roots  (by  osteoclasts)  the 
permanent  tooth  grows  up  into  its  place. 

There  are  six  permanent  teeth  in  each  jaw  which  do  not  succeed 
milk-teeth  ;  these  are  the  permanent  molars.  They  are  developed  from 
an  extension  backwards  on  each  side  of  the  jaw  of  the  original  epithelial 
thickening  or  common  dental  germ  and  by  the  downgrowth  from  this 
into  the  corium  of  three  successive  special  germs  at  comparatively  long 
intervals  of  time.  Within  these  the  tissues  of  the  permanent  molars 
become  formed  in  a  manner  exactly  similar  to  that  in  which  the 
milk-teeth  are  developed. 


THE   TONGUE.  275 


LESSON    XXIX. 

THE  TONO  UE  A  ND  THE  G  USTA  TOR  Y  ORG  A  NS.  THE  M  UCO  US 
MEMBRANE  OF  THE  MOUTH.  THE  PHARYNX  AND 
(ESOPHAGUS. 

1.  Sections  of  the  tongue  vertical  to  the  surface,  stained  with  hsematoxylin 
and  eosin.  The  sections  should  be  taken  from  difterent  parts  and  include  all 
three  kinds  of  papillae. 

2.  Sections  of  injected  tongue. 

3.  Sections  of  the  papilla  foliata  of  the  rabbit,  stained  with  hsematoxylin 
and  eosin  to  show  the  taste-buds  in  situ. 

The  cells  composing  the  taste-buds  are  studied  by  teasing  osmic  prepara- 
tions of  the  papilla  foliata  ;  the  nerve-endings  are  seen  in  sections  of  papillae 
foliatas  which  have  been  treated  by  Golgi's  osmic-bichromate  silver  method. 

4.  Sections  of  the  pharynx  and  of  the  oesophagus  stained  with  hsema- 
toxylin and  eosin. 


The  tongue  is  mainly  composed  of  striated  muscular  fibres,  running 
some  longitudinally,  and  others  transversely.  It  is  covered  by  a  mucous 
membrane,  the  epithelium  of  which,  like  that  of  the  rest  of  the  mouth, 
is  thick  and  stratified,  and  conceals  microscopic  papillae  (fig.  330)  like 
those  of  the  skin.  Besides  these,  the  upper  surface  of  the  organ  is 
covered  with  larger  papillae,  which  give  it  a  rough  appearance.  These, 
which  are  termed  the  lingual  papillce,  are  of  three  kinds:  (1)  About 
twelve  or  thirteen  comparatively  large  circular  projections,  each  of 
which  is  surrounded  by  a  narrow  groove  (fossa),  external  to  which 
the  mucous  membrane  is  raised  above  the  general  level  (vallum) 
(fig.  331).  These  papillae  form  a  V-shaped  line  towards  the  back  of 
the  tongue ;  they  receive  filaments  of  the  glosso-pharyngeal  nerve, 
and  have  taste-buds  in  the  epithelium  which  covers  their  sides,  and 
in  that  of  the  side  of  the  vallum.  They  are  known  as  the  circumvallate 
papillce.  (2)  All  the  rest  of  the  papillary  surface  of  the  tongue  is 
covered  by  conical  pajnllce,  so  named  from  the  conical  pointed  cap  of 
epithelium  which  is  borne  by  each ;  sometimes  this  cap  is  fringed 
with  fine  epithelial  filaments,  when  they  are  termed  filiform  (fig.  332). 
(3)  Scattered  here  and  there  amongst  the  conical  papillae  are  other 
larger  papillae,  the  fungiform  (fig.  333).  These  are  very  vascular,  and 
lie  partly  embedded  in  little  depressions  of  the  mucous  membrane. 

Small  tubular  glands  may  be  seen  between  the  superficial  muscular 
fibres  sending  their  ducts  to  the  surface.     Most  of  them  secrete  mucus, 


276 


THE   ESSENTIALS   OF   HISTOLOGY. 


but  those  which  open  into  the  trenches  of  the  circumvallate  papillae, 
and  a  few  others  elsewhere,  yield  an  albuminous  secretion  (serous 
glands,  glands  of  Elmer). 


Fig.  330.— Section  of 
mucous  membraxe 
of  mouth,  showing 
three  microscopic 
papill.e  and  stra- 
tified    epithelium. 

The       BLOOD-VESSELS 
HAVE  BEEN  INJECTED. 

(Toldt.) 


Fig.  331. — Section  of  circumvallate  papilla, 
HUMAN.  The  figure  includes  ONE  SIDE  of  the 
papilla  and  the  adjoining  part  of  the 
VALLUJI.  (Magnified  150  diameters. )  (Heitzmann.) 

E,  epithelium  ;  G,  taste-bud ;  C,  corium  witli  injected 
blood-vessels  ;  M,  gland  with  duct. 


Fig.  332. — Section  of  two  filiform 

PAPILL.E,  HUMAN.     (Heitzmann.) 

E,  epithelium  ;  C,  corium  ;  L,  lymphoid 

tissue  ;  31,  muscular  fibres  of  tongue. 


Fig.  333. — Section  of  fungiform  papilla, 
HUMAN.  (Heitzmann.)  (Letters  as  in 
previous  figure.) 


THE   TASTE-BUDS. 


277 


The  mucous  membrane  at  the  back  of  the  tongue  contains  a  large 
amount  of  lymphoid  tissue. 

Taste-buds.  -The  minute  gustatory  organs  which  are  known  as  taste- 
huds  or  taste-bulbs  may  be  seen  in  sections  which  pass  through  the 
papillae  vallata^  or  the  papillae  fungiformes ;  they  are  also  present  here 
and  there  in  the  epithelium  of  the  general  mucous  membrane  of  the 


Fig.  334. 


-TONfiUE   OF    RABBIT,    SHOWING   THE    SITUATION    OF   THE 
PAPILLAE   FOLIAT.K.   p. 


tongue,  especially  at  the  back  and  sides,  and  occur  also  upon  the  under 
surface  of  the  soft  palate,  and  on  the  epiglottis.  But  they  are  most 
easily  studied  in  the  papillae  foliatae  of  the  rabbit,  two  small  oval  areas 
lying  on  either  side  of  the  back  of  the  tongue  and  marked  transversely 
with  a  number  of  small  ridges  or  laminae  with  intervening  furrows  (see 


;:^^%4^^^ 


.,',>J'<ria 


^"^^•iOj:- ez- 


Fig.  .33.5. — Vertical  section  of  papilla  foliata  of  the  rabbit,  passing 
ACROSS  THE  FOLI^.     (Ranvier. ) 
p.  central  lamina  of  the  coriuni  ;  v,  section  across  a  vein,  which  traverses  the  folium  ; 
p' ,  lateral  lamina  in  which  the  nerve-fibres  run  ;  <?,  taste-bud  ;  n,  sections  of  nerve- 
bundles  ;  a,  serous  gland. 

fig.  334).      Sections  across  the  ridges  show  numerous  taste-buds  em- 
bedded in  the  thick  epithelium  which  clothes  their  sides  (fig.  335). 

The  taste-buds  are  ovoid  clusters  of  epithelium-cells  which   lie  in 
cavities  in  the  stratified  epithelium  (fig.  336).     The  base  of  the  taste- 


278 


THE   ESSENTIALS   OF   HISTOLOGY. 


bud  rests  upon  the  corium  of  the  mucous  membrane,  and  receives  a 
branch  of  the  glosso-pharyngeal  nerve ;  the  apex  is  narrow  and  com- 
municates with  the  cavity  of  the  mouth  by  a  small  pore  in  the  superficial 
epithelium  {gustatory  poi'e,  fig.  336,  p). 

V         h 


ep 


Fig.  336.— a  taste-bdd  within  the  stratified  epithelium  of  the 

TONGUE.     (Sobotta. )      X  ,W0. 

p,  gustatory  cells  ;  s,  sustentacular  cells  ;  ep,  epithelium  ;  p,  gustatory  pore  ;  h,  hairlets. 


Fig.  337. — Various  cells  from  tastk-bud  of  rabbit.     (Engelmann. ) 

600  diameters. 

rt,  four  gustatory  cells  from  central  part ;  6,  two  sustentacular  cells,  and  one  gustatory 

cell,  in  connection  ;  c,  three  sustentacular  cells. 

The  cells  which  compose  the  taste-buds  are  of  two  kinds,  viz. :  1.  The 
gustoJory  cells  (fig.  337,  a),  which  are  delicate  fusiform  or  bipolar  cells 
composed  of  the  cell  body  or  nucleated  enlargement,  and  of  two  pro- 
cesses, one  distal,  the  other  proximal.  The  distal  process  is  nearly 
straight,  and  passes  towards  the  apex  of  the  taste-bud,  where  it 
terminates  in  a  small,  highly  refracting  cilium-like  appendage,  which 
projects  into  the  gustatory  pore  above  mentioned,  but  the  cell-body 
does  not  itself  quite  reach  the  pore.  The  proximal  process  is  more 
delicate  than  the  other,  and  is  often  branched  and  varicose.  The 
nerve-fibres  (fig.  338)  terminate  in  ramifications  amongst  the  gustatory 
cells  (Retzius).  2.  The  sustentacular  cells  (fig.  337,  c),  which  are 
elongated  cells,  mostly  flattened,  and  pointed  at  their  ends  ;  they  lie 


MUCOUS  MEMBRANE  OF  THE  MOUTH. 


279 


between  the  gustatory  cells,  which  they  thus  appear  to  support,  and 
in  addition  they  form  a  sort  of  envelope  or  covering  to  the  taste-bud. 
Between  the  cells  of  the   taste-bud  lymph-corpuscles  are  often  seen, 


Fig.  338. 


Fig.  339. 


Fig.  338.— Nkrve-endings  in  taste-buds.     (G.  Retzius.) 

-/!,  nerve-fibres  ;  6,  taste-buds  in  outline  ;  i,  ending  of  fibrils  within  taste-bud ;  p,  ending 

in  epithelium  between  taste-buds  ;  s,  sulcus  into  which  the  gustatory  pores  open. 

Fig.  339. — Section  of  the  human  (esophagus.  (Horsley.) 
The  section  is  transverse,  and  from  near  the  middle  of  the  gullet,  a,  fibrous  covering ; 
6,  divided  fibres  of  the  longitudinal  muscular  coat ;  c,  transverse  muscular  fibres ; 
d,  submucous  or  areolar  layer ;  e,  muscularis  mucosas  ;  /,  mucous  membrane  with 
papillae  ;  g,  laminated  epithelial  lining  ;  k,  mucous  gland  ;  i,  gland  duct ;  to',  striated 
muscular  fibres  in  section. 

having  probably  wandered  hither  from  the  subjacent  mucous  membrane. 
Connective  tissue  fibrils  penetrate  between  the  taste-bud  and  the 
stratified  epithelium  in  which  it  is  embedded  (Drasch). 

The  mucous  membrane  of  the  moutli  is  lined  by  a  stratified  epi- 
thelium into  which  numerous  microscopic  vascular  and,  in  some  parts, 
nerve-containing  papillae  project.  The  corium  is  formed  of  connective 
tissue  and  contains  within  and  beneath  it  a  large  number  of  small 
secretory  glands  (buccal  glands).  Most  of  these  secrete  mucus,  but 
some  are  of  the  mixed  type  (see  under  salivary  glands,  p.  286) :  this  is 
the  case,  for  example,  with  the  glands  of  the  lips.  The  ducts  of  the 
buccal  glands  open  everywhere  upon  the  surface  of  the  membrane,  and 
the  openings  of  the  large  ducts  belonging  to  the  salivary  glands  are 
also  seen  at  certain  parts. 


280  THE   ESSENTIALS   OF   HISTOLOGY. 

The  pharynx  is  composed  of  a  fibrous  memhrane  which  is  encircled 
by  striated  muscles,  the  constrictors,  and  lined  by  mucous  membrane. 
The  mucous  membrane  is  covered  on  its  inner  surface  over  the 
upper  part  of  the  pharynx  with  ciliated  epithelium,  which  is 
continuous  with  that  of  the  nostrils,  and  through  the  Eustachian 
tube  with  that  of  the  tympanum.  Below  the  level  of  the  soft  palate 
the  epithelium  is  stratified  like  that  of  the  mouth  and  gullet,  into 
which  it  passes.  In  certain  parts  the  mucous  membrane  contains  a 
large  amount  of  lymphoid  tissue,  and  there  are  numerous  glands 
opening  on  its  surface. 

The  cesophagus  or  gullet,  which  passes  from  the  pharynx  to  the 
stomach,  consists,  like  the  pharynx,  of  a  fibrous  covering,  a  muscular 
coat,  a  lining  mucous  membrane,  and  intervening  connective  tissue  {sub- 
mucous or  areolar  coat)  (fig.  339).  The  muscular  coat  is  much  more 
regularly  arranged  than  that  of  the  pharynx,  and  is  composed  of 
striated  muscle  in  about  its  upper  third  only,  the  rest  being  of  the 
plain  variet3\  There  are  two  layers  of  the  muscular  coat — an  outer 
layer,  in  which  the  fibres  run  longitudinally,  and  an  inner,  in  which 
they  have  a  circular  arrangement.  The  mucous  membrane  is  lined  by 
a  stratified  epithelium,  into  which  microscopic  papillae  from  the  corium 
project.  The  corium  is  formed  of  areolar  tissue,  and  its  limits  are 
marked  externally  by  a  narrow  layer  of  longitudinally  disposed  plain 
muscular  fibres,  the  viuscularis  mvcosce.  This  is  separated  from  the 
proper  muscular  coat  by  the  areolar  coat,  which  contains  the  larger 
branches  of  the  blood-vessels  and  lymphatics,  and  also  the  mucous 
glands  of  the  membrane.  The  ducts  of  these  glands  are  large 
and  usually  pass  through  a  nodule  of  lymphoid  tissue,  lymph-cells 
from  which  infiltrate  the  epithelium  of  the  duct  and  may  pass  out 
into  the  lumen  of  the  duct. 

Besides  these  mucous  glands,  there  are  met  with  both  at  the 
upper  or  laryngeal  part  of  the  oesophagus  and  at  the  lower  or 
cardiac  end  a  certain  number  of  small  tubulo-racemose  glands  of 
a  difi'erent  character.  They  are  confined  to  the  mucous  membrane, 
not  penetrating  the  muscularis  mucosae,  and  their  ducts  open  upon 
and  not  between  the  papilla  of  the  mucous  membrane.  They  closely 
resemble  the  cardiac  glands  of  the  stomach  (see  fig.  353,  p.  290),  and 
it  is  frequently  found  that  the  epithelium  of  the  surface  in  the 
immediate  neighbourhood  of  their  ducts  is  similar  to  that  lining  the 
stomach. 

There  are  two  gangliated  nerve-plexuses,  one  in  the  muscular  coat^ 
and  one  in  the  submucous  coat,  like  those  of  the  intestine  (Klein). 


THE   SALIVARY   GLANDS.  281 


LESSOK    XXX. 
TH?:  SALIVARY  GLANDS. 

1.  Section's  of  the  submaxillary  gland  (dog).  The  gland  may  be  hardened 
in  alcohol  or  formol  and  .>^tained  with  hsematoxylin-eosin  or  with  iron  lijema- 
toxylin  by  Heidenhain's  method.  Notice  the  acini  filled  with  clear  (mucus- 
secreting)  cells,  the  nuclei  of  which  usually  lie  near  the  basement-membrane. 
Notice  here  and  there,  outside  the  clear  cells,  demilunes  or  crescents  of  small 
darkly  stained  granular-looking  (albuminous  i  cells.  Ob.serve  also  the  sections 
of  the  ducts  with  their  striated  columnar  epithelium.  If  possible  find  a 
l)lace  where  one  of  the  ducts  is  passing  into  the  alveoli.  Sketch  under  a 
high  power. 

2.  Study  sections  of  the  parotid  and  sublingual  glands  prepared  in  a 
similar  way,  and  notice  the  diflferences  between  the  three  glands. 

3.  Examine  small  pieces  of  both  submaxillary  and  parotid  gland  of  the 
dog  fresh  in  2  per  cent,  salt  solution.  In  the  submaxillary  gland  notice 
that  the  alveolar  cells  are  swollen  out  with  large  granules  or  droplets  of 
raucigen,  which  swell  up  in  water  to  form  large  clear  vacuoles.  Dilute 
acids  and  alkalies  produce  a  similar  change  but  more  rapidly.  The  cells  of 
the  parotid  gland  are  also  filled  with  granules,  but  they  are  smaller.  The 
granules  are  also  swollen  up  and  dissolved  by  these  fluids.  Make  a  sketch 
from  each  preparation  under  a  high  power. 

4.  To  study  the  changes  which  the  alveolar  cells  undergo  during  secretion, 
pilocarpine  is  administered  to  an  animal  in  sufficient  amount  to  produce 
copious  salivation  ;  after  half  an  hour  the  animal  is  killed  and  its  salivary 
glands  are  examined  as  in  preparation  3.  The  granules  are  not  seen  in  pre- 
parations that  have  been  in  alcohol,  but  osmic  acid  preserves  them  moderately 
well  ;  they  are  well  seen  in  sections  stained  by  Muir's  eosin-methyleue  blue 
method  (see  Appendix). 


The  salivary  glands  may  be  looked  upon  as  typical  of  secreting 
glands  in  general.  They  are  composed  of  a  number  of  lobules  bound 
together  loosely  by  connective  tissue.  Each  small  lobule  is  formed 
of  a  group  of  irregularly  saccular  or  tubular  alveoli  or  acini  from  which 
a  duct  passes,  and  this,  after  uniting  with  other  ducts,  eventually  leaves 
the  gland  to  open  upon  the  surface  of  the  mucous  membrane  of  the 
mouth. 

The  alveoli  are  inclosed  by  a  basement-membrane,  which  has 
flattened  branched  cells  on  its  inner  surface,  next  to  the  epithelium 
(fig.  340).  It  may  be  shown  by  teasing  the  fresh  gland  substance  in 
water  (Langley).  This  basement-membrane  is  continued  along  the 
ducts.  Within  it  is  the  epithelium,  which  in  the  alveoli  is  composed 
of  polyhedral  cells  (fig.  341,  a),  but  in  the  ducts  is  regularly  columnar. 


282 


THE   ESSENTIALS   OF   HISTOLOGY. 


except  in  that  part  of  the  duct  which  immediately  opens  into  the 
alveoli  (junctional  part) ;  in  this  it  is  flattened  (d').  The  columnar 
epithelium  of  the  ducts  is  peculiar,  in  that  the  cells  show  a  distinction 
into  two  unequal  zones,  an  outer,  larger,  striated  zone,  and  an  inner, 
smaller,  granular  one  (fig.  341,  d). 


Fig.  340.  —  Membrana  propria  op  two  alveoli,     (v.  Ebner. )     x600. 
The  preparation  is  taken  from  a  mucous  gland  of  the  rabbit. 

The  cells  of  the  alveoli  diff"er  according  to  the  substance  they  secrete. 
In  alveoli  which  secrete  mucus,  such  as  all  the  alveoli  of  the  dog's 
submaxillary  (fig.  341),  and  some  of  the  alveoli  of  the  same  gland  in 


^-s^fe- 


Fig.  34 L— Section  of  the  submaxillary  gland  of  the  noG,  showing  the 
COMMENCEMENT  OF  A  DUCT  IN  THE  ALVEOLI.     (Magnified  425  diameters. ) 

o,  one  of  the  alveoli,  several  of  which  are  in  the  section  shown  grouped  around  the  com- 
mencement of  the  duct  d' ;  a' ,  an  alveolus,  not  opened  by  the  section  ;  b,  basement- 
membrane  in  section  ;  c,  interstitial  connective  tissue  of  the  gland ;  d,  section  of  a 
duct  which  has  passed  away  from  the  alveoli,  and  is  now  lined  with  characteristically 
striated  columnar  cells  ;  s,  semilunar  group  of  darkly  stained  cells  at  the  periphery 
of  an  alveolus. 

man  (fig.  344),  the  cells,  if  examined  in  normal  saline  solution  or  after 
hardening  with  alcohol,  are  clear  and  swollen.  But  if  examined 
rapidly  in  serum,  or  in  solutions  of  salt  of  from  2  to  5  per  cent., 


THE   SALIVARY  GLANDS. 


283 


they  are  often  seen  to  be  occupied  hy  large  and  distinct  granules 
(Langley).  These  granules  can  also  be  rendered  visible  by  certain 
methods  of  staining,  when  it  is  apparent  that  they  are  not  present  as 
such  in  all  the  cells,  but  have  in  many  cells  become  clear  and  swollen, 
and  converted  into  a  substance  which  is  known  as  mucigen  (fig.  346,  a). 


Fig.  342.— Section  of  a  dog's  submaxillary,  after  a  prolonged  period  of 

REST.     (Ranvier.) 
I,  lumen  of  alveolus  ;  (j,  mucus-secreting  cells  ;  c,  crescent,  formed  of  albiiiwinous  cells. 

Similar  granules  are  seen  also  in  the  cells  lining  the  gland  ducts  ; 
here  also  they  are  found  to  vary  in  size  and  number  with  the  condition 
of  activity  of  the  gland  (fig.  348).  The  mucigen  is  dissolved  out 
of  the  cell  and  discharged  as  mucus  into  the  lumen  of  the  alveolus  and 


','  ^f^ 


Fig.  343. — Submaxillary  of  dog,  after  a  period  of  activity.     (Ranvier.) 

The  mucus-secreting  cells,  g,  have  discharged  their  secretion,  and  are  smaller  and  stain 

better ;  the  albuminous  cells  of  the  crescents,  c,  are  enlarged. 

into  the  ducts,  when  the  gland  is  stimulated  to  activity.  The  cells 
are  known  as  mucous  cells.  But  in  most  alveoli  there  are  some  cells 
which  do  not  contain  mucigen,  but  small  albuminous  granules,  and 
these  often  form  crescentic  groups  which  lie  next  to  the  basement- 
membrane  (figs.   341,  s,  342,  c).      These  are  the  so-called   crescents  of 


284 


Fig.  344.  —Section  of  part  of  the  human  submaxillary  gland. 
(Heidenhain.) 

To  the  right  of  the  figure  is  a  grouj)  of  mucous  alveoli  ;  to  the  left  a  group  of  serous 

alveoli. 


Fig.  345.— Alveoli  of  a  serous  gland.    A,  at  rest.   B,  after  a  short  period 

OF  activity.     C,  after  a  prolonged  period  of  activity.     (Langley.) 

In  A  and  B  the  nuclei  are  obscured  by  the  granules  of  zymogen. 


Fig.  346. —Mucous  cells  from  fresh  submaxillary  glands  of  the  dog. 

(Linjgley.) 

o,  from  a  resting  or  loaded  gland  ;  b,  from  a  gland  which  has  been  secreting  for  some  time  ; 

a',  b',  similar  cells  which  have  been  treated  with  dilute  acid. 


THE   SALIVARY   GLANDS. 


285 


Gianuzzi  ;  their  constituent  cells  are  known  also  as  nuirginal  or  serous 
cells.  Special  diverticula  pass  from  the  lumen  of  the  alveoli  between 
the  mucous  cells  to  penetrate  to  the  crescents  and  to  branch  amongst 
and  within  their  constituent  cells  ;  these  diverticula  are  best  shown  by 


i''"£)..^    "•-.*»>'' 


Fig.  347. — Submaxillary  gland  of  rabbit.     (E.  Miiller.) 
The  cells,  which  are  all  serous,  are  in  different   functional  states,  as  indicated  by  the 
condition  and  staining  of  the  granules.     «,  cell  filled  with  darkly  staining  granules  ; 
b,  clear  cell ;  c,  secretory  canaliculi  penetrating  into  the  cells. 

the  Golgi  method  of  staining  (figs.  349,  350).  They  also  occur  in  the 
purely  serous  alveoli  (fig.  347),  in  which  none  of  the  cells  secrete  mucus, 
but  watery  or  albuminous  saliva.  In  these  when  the  gland  has  been  long 
at  rest  the  cells  are  filled  with  granules,  which  do  not  swell  with  water 


Fig.  348. — Cells  from  duct  of  parotu). 
a,  prior  to  secretion  ;  B,  after  secretion  (Mislawski  and  Smirnow). 

nor  form  mucin;  they  appear  to  be  albuminous  in  nature,  and  prob- 
ably yield  to  the  secretion  of  the  gland  its  ferment  (ptyalin)  and  its 
albumin.  The  granular  substance  within  the  cell  is  not  the  ferment, 
but  the  ferment  is  formed  from  it  when  the  secretion  is  poured  out. 
Hence  it  has  been  termed  zymogen  (mother  of  ferment).     As  Langley 


286 


THE   ESSENTIALS   OF   HISTOLOGY. 


showed,   the   outer  part  of  each    cell    becomes    clear   and   free   from 
granules  after  secretion  (fig.  345). 

Ill  nearly  all  animals  the  parotid  glands  are  composed  of  purely  serous 
alveoli  :  in  man  and  most  animals  the  submaxillary  and  sublingual  glands 
have  both  serous  and  mucous  alveoli  or  "mixed"  alveoli,  i.e.  alveoli  con- 
taining both  serous  and  mucous  cells.  The  smaller  detached  anterior  parts 
of  the  sublingual  gland  have  purely  mucous  alveoli. 


Fig.  34;). — Alveoli  of  human  scblin- 

gttal    glakd   prepared    bv    golgi 

METHOD.     (E.  Miiller. ) 

I,   lumen    stained,   with   lateral   diverticula 

passing    between    mucus-secreting    cells ; 

fi,  longer  diverticula  penetrating  into  the 

"crescent "  cells. 


Fig.  3.50. — Alveoli   of  the  submaxil- 
lary    GLAXD     OF     THE     DOG.       (G. 
Retzius. )    Golgi  method. 
The    extensions    of    the    lumen    into    the 
crescents    of    Gianuzzi    are    shown,   and 
also  the  endings  of  nerve-fibrils. 


The  largest  ducts  have  a  wall  of  connective  tissue  outside  the 
basement>membrane,  and  also  a  few  plain  muscular  cells.  The  blood- 
vessels of  the  salivary  gland  form  a  capillary  network  around  each 
alveolus.  The  lymphatics  commence  in  the  form  of  lacunar  vessels 
between  the  alveoli.  Lymphoid  nodules  are  occasionally  found  in 
the  interstitial  connective  tissue.  The  nerve-fibres,  which  are  derived 
both  from  the  cerebro-spinal  nerves  and  from  the  sympathetic,  pass 
through  ganglia  before  proceeding  to  their  distribution.  They 
ramify  as  fine  varicose  fibrils  amongst  the  alveolar  cells  (fig.  350),  and 
many  are  distributed  to  the  blood-vessels. 

The  salivary  glands  are  developed  as  buds  from  the  epithelium  of  the 
buccal  cavity,  at  first  solid  but  becoming  gradually  hollowed  out.  To 
begin  with  they  are  simple,  but  undergo  ramification  as  they  grow  into 
the  mucous  membrane  and  submucous  tissue. 


THE  STOMACH.  287 


LESSON    XXXI. 
THE  STOMACH. 

1.  Vertical  longitudinal  sections  through  the  cardia,  including  the  lower 
end  of  the  oesophagus  and  the  adjacent  cardiac  portion  of  the  stomach. 
These  are  intended  to  show  the  abrupt  transition  of  the  sti'atified  epithelium 
of  the  oesophagus  into  the  columnar  epithelium  of  the  stomach,  and  also  the 
character  of  the  gastric  and  oesophageal  glands  in  the  immediate  neighbour- 
hood of  the  cardia.     The  sections  may  be  stained  with  hsematoxylin  and  eosin. 

2.  Sections  of  the  fundus  of  the  stomach,  cut  perpendicularly  to  the 
surface  of  the  mucous  membrane. 

In  these  sections  the  general  arrangement  of  the  coats  of  the  stomach  is  to 
be  studied.  Sketches  are  to  be  made  under  a  low  power  illustrating  this 
arrangement,  and  others  under  a  high  power  showing  the  structure  of  the 
glands  of  the  mucous  membrane. 

Measure  the  whole  thickness  of  the  mucous  membrane,  the  thickness  of 
the  muscular  coat,  the  size  of  the  columnar  epithelium-cells  of  the  surface, 
and  that  of  the  cells  in  the  deeper  parts  of  the  glands. 

3.  Sections  of  the  mucous  membrane  of  the  fundus,  cut  parallel  to  the 
surface. 

These  sections  will  show  better  than  the  others  the  arrangement  of  the 
cells  in  the  glands. 

4.  Vertical  sections  of  the  mucous  membrane  from  the  pyloric  region 
of  the  stomach.  If  the  section  is  taken  longitudinally  through  the 
pylorus,  the  transition  of  the  gastric  glands  into  the  glands  of  Brunner 
of  the  duodenum  will  be  made  manifest.  Make  a  sketch  under  a  low  power 
of  one  of  the  glands  in  its  whole  length,  filling  up  some  of  the  details  with 
the  high  power. 

5.  Study  the  arrangement  of  the  blood-vessels  of  the  stomach  in  vertical 
sections  of  the  wall  of  an  organ  the  vessels  of  which  have  been  injected. 


I 


The  wall  of  the  stomach  consists  of  four  coats,  which,  enumerated 
from  without  in,  are  as  follows,  viz.  :  serous,  muscular,  areolar,  or  sub- 
mucous, and  mucous  membrane  (fig.  351). 

The  serous  coat  is  a  layer  which  is  derived  from  the  peritoneum.  It 
is  deficient  only  along  the  lines  of  the  lesser  and  greater  curvatures. 

The  muscular  coat  consists  of  three  layers  of  plain  muscular  fibres. 
Of  these  the  bundles  of  the  outer  layer  run  longitudinally,  those  of 
the  middle  layer  circularly,  and  those  of  the  inner  layer  obliquely. 
The  longitudinal  and  circular  bundles  become  thicker  and  stronger 
towards  the  pylorus  ;  at  the  pylorus  itself  the  circular  layer  is  greatly 
thickened  to  form  a  sphincter  muscle.  The  oblique  fibres  are  only 
present  over  the  fundus. 

The  areolar  or  submucous  coat  is  a  layer  of  areolar  tissue,  which  serves- 


288  THE   ESSENTIALS  OF   HISTOLOGY. 

to  unite  the   mucous  membrane    loosely  to  the  muscular  coat  ;  in  it 

ramify  the  larger  branches  of  the  blood- 
vessels and  lymphatics. 

The  mucous  membraue  is  a  soft   thick 
layer,  generally  somewhat  corrugated  in 
the  empty  condition  of  the  organ.     Its 
inner   surface   is   covered    by   columnar- 
shaped    epithelium    cells,    all    of    which 
secrete  mucus.     They  are  prolonged  into 
the  ducts  of  the  glands,  but  when  these 
divide  to  form  the  tubules  the  cells  be- 
-     "^^     come    cubical,    and    lose     their    mucus- 
secreting    character.      The   thickness   of 
the  mucous  membrane  is  due  to  the  fact 
..  ^^        that  it  is  largely  made  up  of  long  tubular 
\  glands,  which  open  upon  the  inner  sur- 

^_  face.     Between    the   glands   the   mucous 

-^  membrane   is   formed   of    retiform    with 

fc.  y"  some  lymphoid  tissue.     Externally  it  is 

^^1 '   :      -  J  bounded  by  the  vuKCuIaris  mucosce,  which 

&:';.-    -  '  '  consists  of  an  external  longitudinal  and 

S^_  \  \c.n..         an  inner  circular  layer  of  plain  muscular 

J^-  V     '-        -    -  fibres. 

Wt-"  '   :.  Gastric  glands. — These  are  formed  of  a 

J  '■'■  basement-membrane  lined  with  epithelium. 

%--  ;  Each  gland  consists  of  secreting  tubules  from 

|i  ^-m.        one  to  four  in    number,  opening  at  the 

surface  into  a  larger  tube,  the  duct  of  the 

'  '"    '  '"  "' — -'—^^^=^^-  gland.     The  duct  is  in  all  cases  lined  by 

%'hhS^  ^f^c^AxT  oT™f"^"C"««ecreting  epithelium  of  the   same 
STOMACH.    (Mall.)  character  as  that  which  covers  the  inner 

m,  mucous  membrane ;  e,  epithelium  ;  n  c  ai  i  -l    ^  ii. 

rf,  orifice  of  gland-duct ;/».,/(.,  muscu-  surtace  ot  the  mucous  membrane,  but  the 

laris  mucosa;:  sm.,  submucosa :  cm..        -.it  i?    ^i  i.-  j.    i_     i 

circular  muscular  layer ;   Lni./longi-  epithehum     Ot     the     SCCretlUg     tubulCS      IS 

tudmai  muscular  layer;  .,  serous  different  from  this,  and  also  differs  some- 

what  in  the  glands  of  diti'erent  regions  of 
the  organ.     The  following  varieties  of  gastric  glands  are  met  with  : — 

(1)  Glands  of  the  cardia. — These  are  found  in  man  close  to  the  oeso- 
phageal opening  or  cardia ;  they  are  of  two  kinds  :  (a)  simple  tubules, 
very  similar  to  the  crypts  of  Lieberkiihn  of  the  intestine  and  (b)  small 
tubulo-racemose  glands  (fig.  353).  The  secreting  tubules  of  the  race- 
mose glands  are  lined  by  cells  which  are  granular  in  appearance  and  of 
-a  short  columnar  form,  and  of  the  same  nature  throughout  the  length 


THE   STOMACH. 


'289 


of  the  tubule,  except  near  the  orifice  (duct),  where  they  give  place  to 
columnar  mucus-secreting  cells.  Occasionally  one  or  two  oxyntic  cells 
may  be  present  in  their  tubules. 

(2)  Ghouls  of  the  fundus  (oxi/ntic  glands)  (figs.  354,  .355). — In  these 
glands  the  tubules  are  long  and  the  duct  short.  The  epithelium  of  the 
tubules  is  composed  of  two  kinds  of  cells.     Those  of  the  one   kind, 


^^^Hf" 


Fig.  352. — Section  of  the  junction  of  the  (esophageal  and  gastric  mucous 
MEMBRANE  OF  THE  KANGAROO.     (135  diameters.) 

S,  stratified  epithelium  of  tesophagus  abruptly  discontinued  at  S' ;  c,  columnar  epi- 
thelium of  gastric  mucous  membrane  ;  d,  orifices  or  ducts  of  cardiac  glands  ;  m, 
corium  of  oesophageal  mucous  membrane  sending  papillie  into  the  eijithelium; 
rn',  corium  of  gastric  mucous  membrane. 


which  form  a  continuous  lining  to  the  tubule,  are  somewhat  poly- 
hedral in  shape,  and  in  stained  sections  look  clearer  and  smaller 
than  the  others,  but  in  the  fresh  glands,  and  with  certain  methods 
of  staining,  it  can  be  seen  that  they  are  filled  with  granules 
(fig.  355).  The  granules  are  most  numerous  at  the  inner  part  of 
the  cell,  an  outer  zone  being  left  clear.  After  prolonged  activity  this 
outer  zone  increases  in  size  while  the  granules  diminish  in  number  as 

T 


290  .  THE   ESSENTIALS   OF   HISTOLOGY. 

in  the  analogous  cases  of  the  pancreas  and  parotid  glands  (Langley). 
The  cells  are  believed  to  form  pepsin,  and  are  termed  the  cMef  cells 
of  the  cardiac  glands,  or  from  their  relative  position  in  the  tubule 
immediately  surrounding  the  lumen,  the  central  cells.  Scattered  along 
the  tubule,  and  lying  between  the  chief  cells  and  the  basement-mem- 
brane, are  a  number  of  large  spheroidal  or  ovoidal  cells.  These 
are  the  parietal  or  ozyntic  cells}     Each  parietal  cell  is  surrounded  and 


.-t:^^ ' 


^5 


-iscs^ms^-- 


FiG.  353. — Section  of  human  STO^rACH  near  the  cardia.     (v.  Ebner,  after 

J.  Schafifer.)      x4o. 
c,  cardiac  glands  ;  d,  their  ducts  ;  cr,  glands  similar  to  crypts  of  Licberklihn,  with  goblet 

cells;  inm,  mucous  membrane;   ia,  muscularis  mucosae;  !«',  muscular  tissue  within 

mucous  membrane. 

penetrated  by  a  network  of  minute  passages,  communicating  Avith  the 
lumen  of  the  gland  b}^  a  fine  canal,  which  passes  between  the  central 
cells  (fig.  356) ;  but  in  the  neck  of  the  gland  the  parietal  cells  abut 
against  the  lumen,  being  here  wedged  in  betAveen  the  mucus-secreting 
cells  (fig.  354,  A). 

(3)  Glands  of  the  pyloric  canal  (fig.  357). — In  the  glands  of  the  pjdoric 
canal  the  ducts  are  much  longer  than  in  those  of  the  fundus,  and  the 
secreting  tubules  possess  cells  of  only  one  kind.-     These  correspond  to 

^  So  called  because  they  are  believed  to  produce  the  acid  of  the  gastric 
secretion. 

-  In  man  it  is  only  quite  near  the  pylorus  that  oxyntic  cells  are  altogether 
absent. 


GASTRIC   GLANDS. 


291 


t 


Fia.  354. — Sections  of  the  mucous  membrane  ov  the  fundus  of  the  dog's 

STOMACH   passing    ACROSS    THE    LONG   AXIS   OF  THE   GLANDS. 

A,  Section  close  to  but  not  quite  parallel  with  the  surface,  and  including  on  the  left 

the  gland  ducts  and  on  the  right  the  commencing  gland  tubules.     Notice  the  oxyntic 
cells  beginning  to  appear  between  the  columnar  cells  of  the  ducts. 

B,  Deeper  part  of  the   same   section,  showing  the  lumina  of   the  gland  tubules  sur- 

rounded by  chief  cells,  with  the  oxyntic  cells  altogether  outside  them. 


292 


THE   ESSENTIALS  OF   HISTOLOGY. 


the  chief  cells  of  the  fundus  glands,  but  are  not  quite  identical  with 
them  in  appearance,  the  granules  being  much  less  distinct.  The  cells 
are  of  a  columnar  or  cubical  shape,  and  in  the  fresh  condition  of  a 
granular  appearance ;  quite  unlike  the  clear  columnar  epithelium  of  the 


Fig.  355. 


Fig.  356. 


Fig.  357. 


Fig.  355. — A  fundus  gland  of  simple  form  from  the  bat's  stomach. 
Osinic  acid  preparation.     (Langlej*.) 
c,  columnar  epithelium  of  the  surface ;  n,  neck  of  the  gland  witli  central  and  parietal 
cells  ;  ./',  base,  occupied  only  by  principal  or  central  cells,  which  exhibit  the  gi'anules 
accumulated  towards  the  lumen  of  the  gland. 

Fig.  356.  —A  fundus  gland  prepared  by  golgi's  method,  showing  the 

MODE  OF  communication  OF  THE  PARIETAL  CELLS  WITH  THE  GLAND-LUMEN. 

(E.  Muller.) 

Fig.  357. — A  pyloric  gland,  from  a  section  of  the  dog's  stomach.     (Ebstein.) 
in,  mouth  ;   n,  neck  ;   tr,  a  deep  portion  of  a  tubule  cut  transversely. 

surface,  which  is  formed,  as  elsewhere,  of  long  tapering  cells,  the  outer 
part  of  which  is  filled  with  mucigen. 

At  the  pylorus  itself  the  gastric  glands  become  considerably 
lengthened  and  enlarged,  and  are  continued  into  the  submucous 
tissue,    the    muscularis    mucosae    being    here    deficient ;     they    thus 


GASTRIC  GLANDS. 


293 


Fig.  358.— Section  through  the  pylorus,  including  the  commencement  of 
THE  duodenum.     (Klein.) 

r,  villi  of  duodenum  ;  /),  apex  of  a  lymphoid  nodule  ;  c,  crypts  of  Lieberktilin  ;  s,  secreting 
tubules  of  Brunner's  glands  ;  d,  ducts  of  pyloric  glands  of  the  stomach  ;  g,  tubes  of 
these  glands  in  mucous  membrane  ;  (,  deeper  lying  tubes  in  submucosa,  correspond- 
ing to  secreting  tubules  of  Brunner's  glands  of  duodenum  ;  m,  muscularis  mucosae. 


I''    if)  iYmTt7«rTf4iU,\ ;y, )  h  , 


Fig.  .359.— Plan  of  the  blood- 
vessels OF  THE  STOMACH. 
(Modified  from  Brinton. ) 

a,  small  arteries  passing  to  break  up 
into  the  fine  capillary  network,  d, 
between  the  glands ;  b,  coarser 
capillary  network  around  the 
mouths  of  the  glands;  c,  c,  veins 
passing  vertically  downwards  fron^ 
the  superficial  network  ;  e,  larger 
vessels  in  the  submucosa. 


Fig.   360.— Lymphatics    op  the  human  gastric 

MUCOUS  membrane,  injected.     (C.  Lov^n.) 
The  tubules  are  only  faintly  indicated  ;   fi,  muscularis 

mucosas ;  b,  plexus  of  fine  vessels  at  base  of  glands  ; 

c,  plexus  of  larger  valved  lymphatics  in  submucosa. 


294  THE   ESSENTIALS  OF  HISTOLOGY. 

present  transitions  to  the  glands  of  Brunner,  which  lie  in  the  sub- 
mucous tissue  of  the  duodenum  (fig.  358). 

Scattered  amongst  the  ordinary  secreting  cells  of  the  pyloric  glands,  cells 
are  seen  here  and  there  which  stain  differently  from  the  rest,  and  probably 
have  a  different  function  (Stohr).  Occasionally  oxyntic  cells  are  met 
with  in  the  pyloric  glands  and  even  in  Bruinier's  glands  in  the  duodenum 
(Kaufmann). 

The  blood-vessels  of  the  stomach  are  very  numerous,  and  pass  to  the 
organ  along  its  curvatures.  The  arteries  traverse  the  muscular  coat, 
giving  off  branches  to  the  capillary  network  of  the  muscular  tissue, 
and  ramify  in  the  areolar  coat.  From  this,  small  tortuous  arteries 
pierce  the  muscularis  mucosae,  and  break  up  into  capillaries  near  the 
bases  of  the  glands  (fig.  359).  The  capillary  network  extends  between 
the  glands  to  the  surface,  close  to  which  it  terminates  in  a  plexus  of 
relatively  large  venous  capillaries  which  encircle  the  mouths  of  the 
glands.  From  this  plexus  straight  venous  radicles  pass  through  the 
mucous  membrane,  pierce  the  muscularis  mucosae,  and  join  a  plexus  of 
veins  in  the  submucous  tissue.  From  these  veins  blood  is  carried 
away  from  the  stomach  by  efferent  veins,  which  accompany  the  enter- 
ing arteries. 

The  lymphatics  (fig.  360)  arise  in  the  mucous  membrane  by  a  plexus 
of  large  vessels  dilated  at  intervals,  and  looking  in  sections  like  clefts 
in  the  interglandular  tissue.  From  this  plexus  the  lymph  is  carried 
into  large  valved  vessels  in  the  submucous  coat,  and  from  these, 
efferent  vessels  run  through  the  muscular  coat  to  reach  the  serous 
membrane,  underneath  which  they  pass  away  from  the  organ.  The 
muscular  coat  has  its  own  network  of  lymphatic  vessels.  These  lie 
between  the  two  principal  layers,  and  their  lymph  is  poured  into 
the  efferent  lymphatics  of  the  organ. 

The  nerves  have  the  same  general  arrangement  and  mode  of  distribu- 
tion as  those  of  the  intestine  (see  next  Lesson). 


THE   SMALL   AND   LARGE   INTESTINE.  295 


LESSONS    XXXII.   AND    XXXIII. 
THE  SMALL  AND  LARGE  INTESTINE. 

1.  Sections  of  the  duodenum,  jejunum,  and  ileum,  vertical  to  the  surface. 
The  three  parts  of  the  intestine  may  be  embedded  in  the  same  paratfin  block, 
anil  the  sections  stained  and  mounted  together.  Choose  a  part  of  the  ileum 
which  includes  a  Peyer's  patch.  Observe  the  nodales  of  lymphoid  tissue 
which  constitute  the  patch  and  which  extend  into  the  submucous  tissue. 
Observe  the  lymphoid  cells  in  the  superjacent  epithelium.  Notice  also  the 
sinus-like  lymphatic  or  lacteal  vessel  which  encircles  the  base  of  each  nodule. 
In  the  duodenum  study  the  glands  of  Eruuner  in  the  submucous  tissue. 
Make  a  general  sketch  of  each  section  under  a  low  power  and  draw  a  villus 
under  the  high  power.  The  general  arrangement  and  structure  of  the 
intestinal  wall  is  to  be  studied  in  these  sections. 

2.  Sections  parallel  to  the  surface  of  the  intestine,  and  therefore  across 
the  long  axis  of  the  villi  and  glands  of  the  mucous  membrane.  In  order 
to  keep  the  sections  of  the  villi  together  so  that  they  are  not  lost  in  the 
mounting,  it  is  necessary  either  to  embed  in  ceiloidin  or,  if  paraffin  be  used, 
to  employ  an  adhesive  method  of  mounting. 

In  this  preparation,  sketch  the  transverse  section  of  a  villus  and  of  some 
of  the  crypts  of  Lieberklihn. 

3.  To  study  the  process  of  fat-absorption,  kill  a  fi'og  two  or  three  days 
after  feeding  with  bacon  fat.  Put  a  very  small  shred  of  the  mucous  mem- 
brane of  the  intestine  into  osmic  acid  (0'5  per  cent.)  and  another  piece  into 
a  mixture  of  2  parts  Miiller's  fluid  and  1  part  osmic  acid  solution  (1  per 
cent.).  After  foity-eight  hours  teased  preparations  may  be  made  from  the 
osmic  acid  preparation,  in  the  same  manner  as  directed  in  Lesson  VIII.,  §  1. 
The  piece  in  MLiller  and  osmic  acid  may  be  left  for  ten  days  or  more  in  the 
fluid.  When  hardened,  sections  are  made  by  the  freezing  method  and 
mounted  in  glycerine. 

4.  Sections  of  small  intestine  the  blood-vessels  of  which  have  been  injected. 
Notice  the  arrangement  of  the  vessels  in  the  several  layeis.  Sketch  carefully 
the  vascular  network  of  a  villus. 

5.  From  a  piece  of  intestine  which  has  been  stained  with  chloride  of  gold 
tear  ofi"  broad  strips  of  the  longitudinal  muscular  coat,  and  mount  them  in 
glycerine.  It  will  generally  be  found  that  portions  of  the  nervous  plexus  of 
Auerbach  remain  adherent  to  the  strips,  and  the  plexus  can  in  this  way  easily 
be  studied. 

From  the  remainder  of  the  piece  of  intestine  tear  off  with  forceps  the  fibres 
of  the  circular  muscular  layer  on  the  one  side,  and  the  mucous  membrane  on 
the  other  side,  so  as  to  leave  only  the  submucous  tissue  and  the  muscularis 
mucosae.  This  tissue  is  also  to  be  mounted  flat  in  glycerine  :  it  contains  the 
plexus  of  Meissner. 

Sketch  a  small  portion  of  each  plexus  under  a  high  power.  The  plexuses 
can  also  be  studied  by  the  methylene-blue  and  reduced  silver  methods  (see 
Appendix). 

6.  Sections  of  the  large  intestine,  perpendicular  to  the  surface.    These  will 


296 


THE   ESSENTIALS  OF   HISTOLOGY. 


show  the  general  structure  and  arrangement  of  the  coats.     Sketch  under  a 
low  power. 

7.  Sections  of  the  mucous  membrane  of  the  large  intestine  parallel  to  the 
surface,  and  therefore  across  the  glands.  Sketch  some  of  the  glands  and  the 
interglandular  tissue  under  a  high  power. 

8.  The  arrangement  of  the  blood-vessels  of  the  large  intestine  may  be 
studied  in  sections  of  the  injected  organ. 


The  wall  of  the  small  intestine  consists,  like  that  of  the  stomach, 
of  four  coats  (fig.  .361). 

The  serous  coat  is  complete  except  over  part  of  the  duodenum. 


gmy 


gls 


mm 


rm 

Fig.  361. — Diagram  of  sjxtion  of  aliment-^ry  tube.     (Sobotta.) 
Z,  lumen  ;  rjini,  glands  of  mucous  membrane  ;  tp,  epithelium  ;  gls,  glands  in  subniucosa ; 
mm,  muscularis  mucosse  ;  sm,  submucous  coat ;  ria,  circular  muscular  layer ;  Im,  longfi- 
tudinal  muscular  layer ;   s,  serous  coat ;   ss,  mesentery ;   gray,  ganglion   of  plexus 
inyentericus  ;  gsm,  ganglion  of  plexus  submucosus. 


The  muscular  coat  is  composed  of  two  layers  of  muscular  tissue,  an 
outer  longitudinal  and  an  inner  circular.  Between  them  lies  a  network 
of  lymphatic  vessels  and  also  the  close  gangliated  plexus  of  iion- 
medullated  nerve-fibres  known  as  the  plexus  myentericus  of  Auerbach. 
The  ganglia  of  this  plexus  may  usually  be  seen  in  vertical  sections  of 
the  intestinal  wall  (in  figs.  365,  369),  but  the  plexus,  like  the  one 
in   the   submucous   coat  immediately   to   be   described,   can    only  be 


THE   SMALL   INTESTINE.  297 

properly  displayed  in  preparations  made  with  chloride  of  gold  (fig. 
362)  or  methylene  blue  or  by  Golgi's  method. 

The  subimccous  coat  is  like  that  of  the  stomach ;  in  it  the  blood-ve-ssels 
and  lacteals  ramify  before  entering  or  after  leaving  the  mucous  mem- 
brane, and  it  contains  a  gangliated  plexus  of  nerve-fibres — the  plexus 
of  Meissner — which  is   finer   than   that  of  Auerbach   and   has   fewer 


Fig.  362. — Auerbach's  plexds,  from  the  muscular  coat  of  the  intestine. 

(Cadiat. ) 

ganglion  cells  (fig.  363).  Its  branches  are  chiefly  supplied  to  the 
muscular  fibres  of  the  mucous  membrane,  but  also  to  the  glands  and 
villi  (fig.  364). 

The  mucous  membrane  is  bounded  next  to  the  submucous  coat  by  a 
double  layer  of  plain  muscular  fibres  {muscularis  mucosce).  Bundles 
from  this  pass  inwards  through  the  membrane  towards  the  inner 
surface  and  penetrate  also  into  the  villi.  The  mucous  membrane 
proper  is  pervaded  with  simple  tubular  glands — the  cri/pfs  of  Lieberkichn 
(figs.   365,   366,   369)  —  which   are   lined   throughout   by  a  columnar 


298 


THE   ESSENTIALS   OF  HISTOLOGY. 


Fig.  363. — Meissner's  plexus  from  the  submucous  coat.     (Cadiat.) 
a,  gauglion  ;  b,  b,  nervous  cords  ;  c,  a  blood-vessel ;  d,  an  entering  lymphatic  nerve. 


Fig.  364. — Nerves  of  the  mucous  membrane  of  the  small  intestine.  (Cajal. 


M,  part  of  Meissner's  plexus  ;  n-f,  small  nerve-cells  and  nerve-fibres  in  the  tissue  of  the 
mucous  membrane  and  villi. 


THE   SMALL   INTESTINE. 


299 


epithelium,  with  scattered  goblet  cells,  like  that  which  covers  the 
general  surface  aiul  the  villi.  At  the  fundus  of  each  crypt  are  a  few 
cells  containing  well-marked  granules  (Paneth).  The  cells  of  the 
glands  show  frequent  mitoses,  and  it  is  believed  that  the  epithelium  of 


A'.l^iiii*     musculans 
muscosa 


ubimtcosa 


--•---■ -;^ 


layer  of 
circular 
muscular  fibres 


;^: 


intermuscular 
layer 

layer  of 
longitudinal 
muscular  fibres 


Fig.  365. —Section  of  the  small  intestine  (jejunum)  of  cat. 
(Magnified  about  40  diameters.) 


the  general  surface  becomes  regenerated  from  them  (Bizzozero).  The 
mucous  membrane  between  these  glands  is  mainly  composed  of 
reticular  tissue,  which  contains  here  and  there  nodules  of  lymphoid 
tissue.  These  nodules  constitute  when  they  occur  singly  the  so-called 
solitary  glands  of  the  intestine  (fig.  368),  and  when  aggregated  together 


300 


THE   ESSENTIALS   OF  HISTOLOGY. 


form   the  agminated  glands  or  patches  of  Peyer  (fig.  374). 
occur  chiefly  in  the  ileum. 


The  latter 


Fig.  367.— Cross-section  ok  a  small 
fragment  of  the  mucous  membrane 
of  the  intestine,  including  one  entire 
crypt  of  lieberkuhn  and  parts  ok 
THREE  OTHERS.  (Magnified  400  dia- 
meters.)    (Frey.) 

a,  cavity  of  the  tubular  glands  or  ci-ypts  ;  6,  one 
of  the  lining  epithelium-cells  ;  c,  the  inter- 
glandular  retifurm  tissue  ;  0.,  lymph-cells. 


Fig.  366. — A  crypt  of  Lie- 

BERKUHN  FROM  THE  HUMAN 

intestine.     (Flemming.) 


Fig.  368. — Section  of  the  ileum  through  a  lymphoid  nodule.     (Cadiat.) 
n,  middle  of  the  nodule  with  the  lymphoid  tissue  jiartly  fallen  away  from  the  section  ; 

b,  epithelium  of  the  intestine  ;  c,  villi :  their  ei^ithelium  is  partly  broken  away  ;  d, 

crypts  of  Lieberkiihn ;   e,  /,  muscularis  mucosas. 


TEE   SMALL   INTESTINE. 


301 


The  glands  of  Brumm;  which  have  been  already  noticed  (p.   294), 
occur  in   the  duodenum.     They  are  small  tubulo-racemose  glands  of 


inds  of 
unner 
sabmucoso. 


circular 
muscular  layer 


**,— '-~^'*'''*S.'^~»« 


Fig.  369. — iSKCTiox  ok  duodenum  ok  cat,  showing  Beunnee's  glands. 
(Magnified  about  60  diameters.) 

serous  character,  situated  in  the  submucosa  (fig.  369) ;  they  send  their 
ducts  to  the  inner  surface  of  the  mucous  membrane  either  between 
the  crypts  of  Lieberkiihn  or  into  them. 


302  THE   ESSENTIALS  OF  HISTOLOGY. 

The  villi  with  which  the  whole  of  the  inner  surface  of  the  small 
intestine  is  closely  beset  are  clavate  or  finger-shaped  projections  of  the 
mucous  membrane,  and  are  composed,  like  that,  of  retiform  tissue 
covered  with  columnar  epithelium  (figs.  370  to  372).  The  characters 
of  this  epithelium  have  already  been  described  (Lesson  VIII.). 
Between  and  at  the  base  of  the  epithelium-cells  many  lymph- 
corpuscles   occur,   as  well  as  in  the  meshes    of  the    retiform   tissue. 


li 


I 


?v 


Fig.  370. — Longitudixal  section  of  a  villus  from  a  kat  killed  three  hours 
after  feeding  with  bread  and  water. 

The  columnar  epithelium  shows  numerous  lymph-corpuscles  between  the  cells  ;  I,  lacteal, 
containing  lymph-corpuscles,  c,  some  partly  disintegrated. 

The  epithelium  rests  upon  a  basement-membrane.  In  the  middle  of 
the  villus  is  a  lymphatic  or  lacteal  vessel  which  may  be  somewhat 
enlarged  near  its  commencement,  but  the  enlargement  is  replaced  in 
some  animals  by  a  network  of  lacteals.  Surrounding  this  vessel  are 
small  bundles  of  plain  muscular  tissi;e  prolonged  from  the  muscularis 
mucosae.  The  network  of  blood-capillaries  (figs.  370,  373)  lies  for  the 
most  part  near  the  surface  within  the  basement-membrane;  it  is 
supplied  with  blood  by  a  small  artery  which  joins  the  capillary 
network  at  the  base  of  the  villus ;  the  corresponding  vein  generally 
arises  near  the  extremity. 


THE   SMALL   INTESTINE. 


303 


■/" 


— /> 


Fig.  371.— Transverse  section  of  x  villus,  man.     (v.  Ebner.)    Magnified 
530  diameters. 
a,  basement-raeinbrane,  here  somewhat   shrunken   away   from   epithelium  ;   6,   goblet- 
cells  ;  c,  cuticula  ;  «/,  lacteal ;  c,  columnar  epithelium  ;  /,  leucocytes  in  epithelium  ; 
r,  leucocytes  below  epithelium  ;  /",  large  leucocytes  ;  g,  blood-vessels. 


Fig.  372.— Part  of  a  section  through  a  villus  op  the  dog,  highly 
MAGNIFIED.     (R.  Heidenhain.) 
jii,  plain  muscle  ;  I,  V,  I",  leucocj'tes,  which  are  seen  in  large  numbers  in  the  interstices 
of  the  reticular  tissue  ;  hi,  vessels  ;  c,  connective-tissue  cells,  covering  the  fibrils  of 
the  reticulum.     The  epithelium  of  the  villus  is  not  represented. 


304 


THE   ESSENTIALS  OF  HISTOLOGY. 


The  lymphatics  (lacteals)  of  the  mucous  membrane  (fig.  374),  after 
receiving  the  central  lacteals  of  the  villi,  pour  their  contents  into  a 
plexus  of  lai'ge  valved  lymphatics  which  lie  in  the  submucous  tissue 
and  form  sinuses  around  the  bases  of  the  lymphoid  nodules  (fig.  256, 


Fig.  373.— Small  intestin'e  (vertical  transverse  section),  with  the 
BLOOD-VESSELS  INJECTED.     (Heitzmanii. ) 

F,  a  villus  ;  G,  glands  of  Lieberkuhn ;  M,  muscularis  mucosse;  A,  areolar  coat ;  R,  circular 
muscular  coat;  L,  longitudinal  muscular  coat;  P,  peritoneal  coat. 

p.  208).  From  the  submucous  tissue  eff"erent  vessels  pass  through  the 
muscular  coat,  receiving  the  lymph  from  an  intramuscular  plexus  of 
lymphatics,  and  are  conveyed  away  between  the  layers  of  the  mesentery. 
Absorption  of  fat. — In  order  to  study  the  process  of  fat  transference 
in  the  intestine,  it  is  convenient  to  stain  the  fat  with  osmic  acid,  which 


ABSORPTION   OF   FAT. 


305 


^     A 


r' 


ML 


Fig.  374.— Vertical  section  of  a  portion  of  a  Peyer's  patch,  with  the 
LACTEAL  VKS.SELS  INJECTED.     Magnified  32  diameters.     (Frey.) 

The  specimen  is  from  the  lower  part  of  the  ileum  ;  a,  villi,  with  their  lacteals  left  white  ; 
6,  some  of  the  tubular  glands ;  c,  the  muscular  layer  of  the  mucous  membrane  ; 
d,  cupola  or  projecting  part  of  the  nodule  ;  e,  central  part ;  /,  the  reticulated  lacteal 
vessels  occupying  the  lymphoid  tissue  between  the  nodules,  joined  above  by  the 
lacteals  from  the  villi  and  mucou.s  surface,  and  passing  below  into  .a,  the  sinus-like 
lacteals  under  the  nodules,  which  again  jmss  into  the  large  efferent  lacteals,  (f  ;  i, 
part  of  the  muscular  coat. 


Fig.  375.— Section  of  the  villu.s  of  a  r.\t  killed  during  fat-absorption. 

ep,  epithelium  ;  .s(r,  striated  border  ;   c,  leucocytes  ;   d ,  leucocytes  in  the  epithelium  ; 
i,  central  lacteal  containing  chyle  and  disintegrating  leucocytes. 

u 


306 


THE  ESSENTIALS   OF   HISTOLOGY. 


colours  it  black.  It  can  then  be  observed  that  in  animals  which  have 
been  fed  with  food  containing  fat,  particles  of  fat  are  present  (1)  in 
comparatively  large  globules  within  the  cohxmnar  epithelium-cells ;  (2) 
in  fine  granules  in  the  interstitial  tissue  of  the  villus,  but  often  confined 
to  the  amoeboid  leucocytes,  which  abound  in  this  tissue ;  (3)  in  fine 
granules  within  the  central  lacteal  of  the  villus.  The  leucocytes  are 
present  not  only  in  the  reticular  tissue  of  the  villus,  but  also  in  con- 
siderable numbers  between  and  at  the  base  of  the  epithelium-cells  ;  and 
they  can  also  be  seen  in  thin  sections  from  bichromate-osmic  prepara- 
tions within  the  commencing  lacteal ;  in  the  last  situation  they  are 
undergoing  disintegration  (figs.  375,  376).  These  observations  are 
easily  made  in  the  frog. 


Fig.  376. — Mucous  meiibr.\ne  of  frog's  intesti.ne  during  fat- absorption. 

ep,  epithelium  ;  sir,  striated  border ;  e,  leucocytes  ;  I,  lacteal. 

Since  the  leucocytes  are  amoeboid,  it  is  probable  from  these  facts 
that  the  mechanism  of  fat-absorption  consists  of  the  following  processes 
— viz.  (1)  absorption  or  formation  of  fat  in  the  columnar  epithelium- 
cells  of  the  surface ;  (2)  ejection  of  fat-granules  from  the  epithelium 
into  the  tissue  of  the  villus;  (3)  inception  of  fat  by  leucocytes, 
these  taking  it  up  after  it  has  passed  out  of  the  epithelium-cells  ;  (4) 
migration  of  leucocytes  carrying  fat  particles  through  the  tissue 
of  the  villus  and  into  the  central  lacteal;  (5)  disintegration  and  solution 
of  the  immigrated  leucocytes,  and  setting  free  their  contents.  Since 
fat-particles  are  never  seen  in  the  striated  border  of  the  columnar 
cell  it  is  probable  that  the  fat  first  becomes  saponified  by  the  action  of 
the  digestive  juices,  and  reaches  the  epithelium-cell  in  the  form  of 
dissolved  soap ;  the  fat  which  is  seen  and  stained  by  osmic  acid  within 
the  cells  having  become  re-formed  by  a  process  of  synthesis. 

In  some  young  animals  (puppy,  kitten)  the  fat  which  is  undergoing 
absorption  is  seen  not  only  in  the  epithelium-cells  and  leucocytes,  but 
also  in  the  form  of  streaks  of  liquid,  stained  black  by  osmic  acid,  in  the 
interstices  of  the  reticular  tissue  of  the  villi.     It  has  probably  passed 


THE   LARGE   INTESTINE. 


307 


k-.^siS^^  -r:i&«^"»%  ^^^- . 


~%J 


7k,' 


Fig.  377.— Glands  of  the  large  inte.stine  of  child.      (300  diameters.) 
A,  in  longitudinal  section  ;  B,  in  transverse  section. 


308  THE   ESSENTIALS  OF  HISTOLOGY. 

out  from  the  epithelium  in  a  dissolved  condition  by  a  kind  of  reversed 
secretion. 

The  migration  of  leucocytes  into  the  lacteals  of  the  villi  is  not 
a  special  feature  of  absorption  of  fat,  but  occurs  also  when  absorp- 
tion of  other  matters  is  proceeding  (fig.  370) ;  the  transference  of 
fat-particles  is  merely  a  part  of  a  more  general  •  phenomenon  of 
migration  of  leucocytes  which  accompanies  the  process  of  absorption. 

The  large  intestine  has  the  usual  four  coats,  except  near  its  termina- 
tion, where  the  serous  coat  is  absent.  In  man  the  mnscular  coat  is 
peculiar  in  the  fact  that  along  the  ca?cum  and  colon  the  longitudinal 
muscular  fibres  are  gathered  up  into  three  thickened  bands  which 
produce  puckerings  in  the  wall  of  the  gut. 

The  mucous  membrane  of  the  large  intestine  is  beset  with  simple 
tubular  glands  somewhat  resembling  the  crypts  of  Lieberkiihn  of  the 
small  intestine,  and  lined  by  columnar  epithelium  similar  to  that  of 
the  inner  surface  of  the  gut,  but  containing  many  more  mucus-secreting 
or  goVjJet-cells  (fig.  377).  The  blind  extremity  of  each  gland  is  usually 
slightly  dilated.  These  glands  of  the  large  intestine  are  not  strictly 
homologous  with  the  crypts  of  the  small  intestine,  for  whereas  the 
latter  are  developed  as  depressions  in  the  general  surface  between  the 
villi,  the  glands  of  the  large  intestine  are  formed  by  the  growing 
together  of  villus-like  projections  of  the  surface.  The  interglandular 
tissue  is  a  reticular  tissue  and  is  beset  here  and  there  with  solitary 
glands,  especially  in  the  ca;cum.  The  mucous  membrane  of  the 
vermiform  appendix  is  in  great  part  of  its  extent  packed  full  of 
lymphoid  nodules. 

The  arrangement  of  the  blood-vessels  and  lymphatics  in  the  large 
intestine  resembles  that  in  the  stomach.  The  nerves  of  the  large 
intestine  also  resemble  those  of  the  stomach  and  small  intestine  in 
their  arrangement. 

At  the  lower  end  of  the  rectum  the  circular  muscular  fibres  of  the 
gut  become  thickened  a  little  above  the  anus  to  form  the  internal 
sphincter  muscle.  In  the  anal  region  there  are  a  number  of  compound 
racemose  mucous  glands  opening  on  the  surface  of  the  mucous  mem- 
brane (anal  glands).  The  anus  has  a  lining  of  stratified  epithelium 
continuous  with  that  of  the  skin. 


THE   LIVER.  309 


LESSONS   XXXIV.   AND    XXXV. 
THE  LIVER   AND  PANCREAS. 

1.  Sections  of  liver  are  to  be  studied  carefully.  They  may  be  stained  with 
eosiu  and  hasmatoxylin ;  or  by  eosin  and  niethyleiie-blue  after  Muir's 
method  (see  Appendix).  Sketch  the  general  arranoement  of  the  cells  in  a 
lobule  under  the  low  power;  Hud  under  the  high  power  make  very  careful 
drawings  of  .some  of  the  hepatic  cells  and  also  of  a  portal  canal.  If  from  the 
pig,  the  outlines  of  the  lobules  are  observed  to  be  very  well  marked. 

Notice  that  the  hepatic  cells  are  in  intimate  contact  with  rhe  blood-capil- 
laries or  sinusoids.  Some  cells  may  be  found  to  contain  red  blood-corpuscles  ; 
many  are  filled  with  eosinophil  granules.  Notice  in  the  sinusoid  capillaries 
the  large  partly  detached  endothelial  cells  (cells  of  Kuptfer).  These  also 
frequemly  contain  erythrocytes,  which  ajjpear  to  be  in  process  of  destruction. 

2.  To  observe  the  glycogen  within  the  liver-cells,  kill  a  rabbit  or  rat  (pre- 
ferably about  six  hours  after  a  full  meal  of  carrot),  and  at  once  throw  a  thin 
piece  of  the  liver  into  9(5  per  cent,  alcohol.  When  well  hai-dened  the  piece 
may  be  embedded  in  paraffin  in  the  usual  way,  or  sections  may  be  cut  with 
the  free  hand  without  embedding.  Some  of  the  sections  so  obtained  are  to 
be  treated  with  a  1  per  cent,  sulution  of  iodine  in  potassium  iodide  for  five 
minutes  ;  they  may  then  be  mounted  in  a  nt-arly  saturated  solution  of  potas- 
sium acetate,  the  cover-gl;i.ss  being  cemented  with  gold  size. 

3.  Presence  of  iron.  Other  sections  of  alcohol-hardened  liver  are  to  be 
treated  first  with  potassium  ferrocyanide  solution  and  then  with  hydrochloric 
acid  and  alcohol  (1  to  10),  passed  through  absolute  alcohol  into  xylol,  and 
mounted  in  dammar ;  in  these  many  of  the  pigment  granules  will  be 
stained  blue  (Prussian  blue).  Or  the  sections  may  simply  be  placed  in  an 
aqueous  solution  of  hsematoxylin  (1  to  300),  with  or  without  previous  treat- 
ment with  alcohol  containing  10  parts  per  cent,  hydrochloric  acid  (to  set 
free  organically  combined  iron),  after  which  they  are  mounted  in  the  ordinary 
way  (Macallum's  method). 

■  4.  Study,  first  with  the  low  power  and  afterwards  with  the  high  power, 
a  section  of  the  liver  in  which  the  blood-vessels  have  been  injected.  Almost 
invariably  the  injection  will  be  found  to  have  penetrated  into  canaliculi 
within  the  liver-cells  themselves.  Make  a  general  sketch  of  a  lobule  under 
the  low  power  and  liraw  a  small  part  of  the  network  of  blood-vessels  and 
intracellular  canaliculi  under  the  high  power. 

5.  Take  a  small  piece  of  liver  which  has  been  several  weeks  in  2  per  cent, 
bichromate  of  potassium  solution  or  Mliller's  fluid  and  plunge  it  in  1  per 
cent,  nitrate  of  silver  solution,  changing  the  fluid  after  half  an  hour.  Leave 
the  piece  of  liver  in  the  silver  solution  overnight.  It  may  then  be  trans- 
ferred to  alcohol,  and  after  complete  dehydration  embedded  and  cut  in 
parafiin  in  the  usual  way  and  the  sections  mounted  in  dammar.  In  many 
parts  of  such  sections  the  bile-canaliculi  are  stained. 

They  can  also  be  brought  to  view  (at  the  periphery  of  the  lobules)  by 
injection  with  solution  of  Berlin  blue  from  the  hepatic  duct  ;  or,  throughout 
the  whole  of  the  lobule,  by  injecting  about  60  c.c.  of  saturated  sulphindi- 
gotate  of  soda  solution  in  three  successive  portions,  at  intervals  of  half  an 


310 


THE   ESSENTIALS   OF  HISTOLOGY. 


hour,  into  the  blood-vessels  of  an  anj&sthetized  cat  or  rabbit.  Two 
hours  after  the  last  injection  the  animal  is  killed,  and  the  blood-vessels 
washed  out  with  saturated  solution  of  potassium  chloride.  The  organ  is 
then  fixed  with  absolute  alcohol.  But  the  chromate  of  silver  method  is 
easier  and  surer  than  the  injection  methods. 

6.  Tease  a  piece  of  fresh  liver  in  serum  or  salt  solution  for  the  study  of 
the  appearance  of  the  hepatic  cells  in  the  recent  or  living  condition. 

7.  Stained  sections  of  pancreas  from  a  gland  which  has  been  hardened  in 
alcohol,  or  in  formol  followed  by  alcohol.  The  sections  may  be  double 
stained  with  eosin  and  hsematoxylin  or  with  eosin  and  methylene  blue. 
Notice  the  islets  of  Langerhans  between  the  alveoli  ;  largest  and  most 
evident  in  animals  which  have  been  long  fasting  and  also  very  well  marked 
after  the  gland  has  been  stimulated  by  secretin. 

Make  sketches  under  both  low  and  liigh  power. 

8.  Tease  a  small  piece  of  fresh  pancreas  in  serum  or  salt  solution.  Notice 
the  granules  in  the  alveolar  cells,  chiefly  accumulated  in  the  half  of  the  cell 
which  is  nejirest  the  lumen  of  the  alveolus,  leaving  the  outer  zone  of  the 
cell  clear. 

Sketch  a  small  portion  of  an  alveolus  under  a  high  power. 

9.  The  ducts  of  the  pancreas,  and  the  termination  of  nerve-fibres  in  the 
alveoli  may  be  seen  in  preparations  made  by  the  Golgi  method. 


THE  LIVER. 
The  liver  is  a  solid  glandular  organ,  made  up  of  the  hepatic  lobules. 
These  are   polyhedral   masses   (tig.   .378)  about    1    mm.   {^-^  inch)   in 


Fig.  378. — Diagrammatic  representation  of  two  hkpatic  lobules. 
The  left-hand  lobule  is  rejii-esented  with  the  intralobular  vein  cut  across ;  in  the  right- 
hand  one  the  section  takes  the  course  of  the  intralobular  vein,  p,  interlobular 
branches  of  the  portal  vein  ;  /(,  intralobular  branches  of  the  hepatic  veins  ;  s,  sub- 
lobular  vein  ;  c,  capillaries  of  the  lobules.  The  arrows  indicate  the  direction  of  the 
course  of  the  blood.     The  liver-cells  are  only  represented  in  one  part  of  each  lobule. 


diameter,  composed  of  cells,  and  separated  from  one  another  by 
connective  tissue.  In  some  animals,  as  in  the  pig,  this  separation 
is  complete,  and  each  lobule  is  isolated,  but  in  man  and  mo.st  animals 
it  is  incomplete.     There  is  also  a  layer  of  connective  tissue  underneath 


THE   LIVER. 


311 


the  serous  covering  of  the  liver,  forming  the  so-called  capsule  of  the 
organ.  Each  lobule  is  penetrated  by  a  fine  network  of  reticular 
tissue  which  helps  to  support  the  columns  of  cells  within  the  lobule 
(fig.  379). 

The  afferent  blood-vessels  of  the  liver  (portal  vein  and  hepatic  artery) 
enter  it  on  its  under  surface,  where  also  the  bile-duct  passes  away  from 
the  gland.  The  branches  of  these  three  vessels  accompany  one  another 
in  their  course  through  the  organ,  and  are  inclosed  by  loose  connective 


Fig.  379.  —Reticulum  of  a  liver-lobule.     (Oppel. 
V.C..,  central  vein  ;  i,  interlobular  interval. 

tissue  (capsule  of  GUssm),  in  which  are  lymphatic  vessels,  the  whole 
being  termed  a  portal  canal  (fig.  380).  The  smaller  branches  of  the 
vessels  penetrate  to  the  intervals  between  the  hepatic  lobules,  and 
are  known  as  the  interlobular  branches.  The  blood  leaves  the  liver 
at  the  back  of  the  organ  by  the  hepatic  veins ;  the  branches  of 
these  run  through  the  gland  unaccompanied  by  other  vessels  (except 
lymphatics)  and  can  also  be  traced  to  the  lobules,  from  each  of 
which  they  receive  a  minute  branch  (central  or  intralobular  vein) 
which  passes  from  the  centre  of  the  lobule,  and  opens  directly  into 
the  (sublobular)  branch  of  the  hepatic  vein. 

Each  lobule  is  a  mass  of  hepatic  cells  pierced  everywhere  with  a 


312  THE   ESSENTIALS   OF  HISTOLOGY. 

network  of  sinusoid  blood-vessels,  the  so-called  hepatic  capillaries 
(fig.  378),  which  at  the  periphery  of  the  lobule  receive  blood  from  the 
interlobular  branches  of  the  portal  vein  {p),  and  converge  to  the  centre 
of  the  lobule,  where  they  unite  to  form  the  intralobular  branch  of  the 
hepatic  vein.  The  interlobular  branches  of  the  hepatic  arteries  join 
this  network  a  short  distance  from  the  periphery  of  the  lobule.  The 
blood-capillaries  are  in  direct  contact  with  the  liver-cells  ;  indeed,  it 
would  appear  as  if  the  endothelium  is  deficient,  for  artificial  injections 
are  seen  to  be  in  contact  with  the  cells  and  even  pass  between  their 
interstices  and  run  into  canaliculi  within  their  protoplasm.  The 
endothelium   of  the   blood-vessels  (or  sinusoids)  is   in   part  at  least 


Fig.  380.— Section  of  a  portal  canal. 

a,  branch  of  hepatic  artery  ;  v,  branch  of  portal  vein  ;  d,  bile-duct ;  /,  /,  lymphatics  in 
the  areolar  tissue  of  Glisson's  capsule  which  incloses  the  vessels. 

represented  by  certain  conspicuous  cells  which  occur  at  intervals  on 
the  wall  of  the  sinusoids,  and  lie  in  contact  with  the  liver  cells. 
These  cells  were  described  by  Kupffer.  They  are  phagocytic,  like 
the  endothelial  cells  of  the  blood-sinuses  of  the  spleen,  and  ingest 
erythrocytes,  which  can  be  seen  within  them. 

The  hepatic  cells,  which  everywhere  lie  between  and  surround  the 
capillaries,  are  polyhedral,  somewhat  granular-looking  cells,  each 
containing  a  spherical  nucleus.  The  jDrotoplasm  of  each  cell  is 
pervaded  by  an  irregular  network  of  fine  canaliculi  (fig.  383),  which 
in  preparations  of  injected  liver  become  filled  with  the  injection 
material,  w^hich  has  passed  into  them  from  the  blood-vessels  (Herring 
and  Simpson).  They  thus  form  a  system  of  intracellular  canals  which 
probably  receive  the  blood-plasma  directlj^  from  the  vessels.  Such 
canals  were  conjectured  to  exist  by  Browicz,  who  showed  that  under 


THE   LIVER. 


313 


certain  circumstances  not  only  hsemoglobin  but  whole  red  blood- 
corpuscles,  and  even  groups  of  blood-corpuscles,  which  are  in  process 
of  breaking  down,  are  to  be  found  in  the  interior  of  the  hepatic 
cells.  In  the  dog's  liver  both  haemoglobin  and  bilirubin  may  be 
fouiul  in  the  form  of  crystals  within  the  nuclei  of  the  liver-cells 
(Browicz).  It  is  easy  to  inject  these  minute  canals  from  the  blood- 
vessels, and  they  are  clearly  .shown  filled  with  the  injection  mass 
in  the  preparation  of  injected  liver  of  rabbit  shown  in  fig.  384. 
Besides  these   plasma-channels,  the   liver   cells  may  show  fine,  short 


Fig.  381. — Sectiox  of  babbit's  liver  with  the  intercellular  network  of 
BILE-CANALICCLI  INJECTED.      Highly  magnified.      (Hering.) 

Two  or  three  layers  of  cells  are  represented  ;  6,  blood-capillaries. 

canals  which  communicate  with  the  intercellular  bile-ducts  (see  below) 
and  generally  commence  within  the  cell  by  a  dilatation  (secretion- 
vacuoles). 

After  a  meal  many  of  the  liver  cells  may  contain  fat,  and  masses 
of  glycogen  can  also  be  seen  within  them  (fig.  385)  if  the  liver 
be  hardened  in  alcohol  and  treated  in  the  manner  described  in 
section  2.  The  cells  also  contain  pigment-granules,  many  of  which 
are  stained  by  potassium  ferrocyanide  and  hydrochloric  acid,  or  by 
pure  hsematoxylin  (presence  of  iron  ^). 

The  ducts  commence  between  the  hepatic  cells  in  the  form  of  inter- 
cellular bile-canaliculi,   which   lie   between   the   adjacent    sides   of  the 

'  The  iron  which  is  in  organic  combination  can  be  set  free  by  treatment  for  a 
short  time  with  alcohol  to  which  10  p.c.  hydrochloric  acid  has  been  added. 


314 


THE   ESSENTIALS  OF   HISTOLOGY. 


cells,  and  receive  the  contents  of  the  secretion-vacuoles  above 
mentioned.  They  form  a  network,  the  meshes  of  which  correspond 
in  size  to  the  cells  (fig.  381),  and  at  the  periphery  of  the  lobule  they 
pass  into  the  interlobular  bile-ducts  (fig.  382).  In  many  animals  the 
network  of  bile-canaliculi  is  incomplete  (G.  Retzius). 


Fig.  382. — Lobule  of  rabbit's  liver  :    vessels  and  bile-ducts  injected. 

(Cadiat.) 

a,  central  vein  ;   '/,  6,  peripheral  or  Interlobular  veins  ;   c,  interlobular  bile-duct.    The 

liver-cells  are  not  represented. 

The  bile-ducts  are  lined  by  clear  columnar  epithelium  (fig.  380,  d). 
Outside  this  is  a  basement-membrane,  and  in  the  larger  ducts  some 
fibrous  and  plain  muscular  tissue.  Many  of  the  large  ducts  are 
beset  with  small  blind  diverticula. 

The  gall-bladder  is  in  its  genei-al  structure  similar  to  the  larger 
bile-ducts.  It  is  lined  hy  columnar  epithelium,  and  its  wall  is 
formed  of  fibrous  and  muscular  tissue. 


THE   LIVER. 


315 


The  lymphatics  of  the  liver  have  been  described  as  commencin<<  as 
perivascuhir  lymphatic  spaces  inclosing  the  capillaries  of  the  lobules 
(MacGillavry),    But  this  cannot  be  so,  since  there  is  no  space  between 


Fig.  383. 


Fig.  384. 


Fig.  383. — A  cell  fkom  the  human  liver,  showing  intracellular 
CANALICULI.     (Browicz.) 

Fig.  384. — From  a  section  of  rabbit's  liver  injected  from  the  portal 

VEIN,     showing    intracellular     CANALICULI     COMMUNICATING    WITH    THE 
INTERCELLULAR   BLOOD-SINUSOIDS. 


Fig.  3S.5.— Liver  cells  containing  glycogen.     (Dunham,  from  Barfurth.) 

the  liver-cells  and  the  sinusoid  capillaries  with  which  they  come  into 
immediate  relationship  (Herring  and  Simpson).  All  that  can  be  posi- 
tively asserted  is  that  there  are  numerous  lymphatics  accompanying  the 
branches  of  the  portal  vein,  and  others,  less  numerous,  accompanying 


316  THE   ESSENTIALS  OF  HISTOLOGY. 

the  tributaries  of  the  hepatic  veins,  but  so  far  as  can  be  ascertained  no 
direct  communication  exists  between  the  two  sets  of  lymphatics  within 
the  lobules,  although  they  communicate  freely  near  their  exit  from 
the  liver.     Most  of  the  lymph  passes  out  by  the  portal  lymphatics. 

Nerves  are  described  as  distributed  both  to  the  blood-vessels  and  to 
the  liver-cells. 

THE    PANCREAS. 

The  pancreas  is  a  tubulo-racemose  gland,  resembling  the  salivary 
glands  so  far  as  its  general  structure  is  concerned,  but  diifering  from 


6-;- 


Fig.  386. — Section  Of  human  p.^nckeas.     (Bohm  and  v.   DavidofF.)    ^p. 

a,  group  of  cells  in  interstiti.al  tissue  (islet  of  Langerhans)  ;  6,  connective  tissue  ;  c,  larper 
duct ;  d,  d,  alveoli  with  centro-acinar  cells  ;  c,  small  duct  passing  into  alveoli ;  /,  inner 
granular  zoue  of  alveolus. 

them  in  the  fact  that  the  alveoli  are  longer  and  more  tubular  in 
character.  Moreover,  the  connective  tissue  of  the  gland  is  somewhat 
looser,  and  there  occur  in  the  glandular  sub.stance  here  and  there 
small  groups  of  epithelium-like  cells  unfurnished  with  ducts  {islets 
of  Langerhans)  (fig.  386  a ;  fig.  387),  which  are  supplied  with  a 
close  network  of  large  convoluted  capillary  vessels  (fig.  388).  Their 
function  is  unknown,  but  their  presence  is  very  characteristic  of  the 
pancreas.  They  increase  in  size  during  starvation  and  also  as  the 
result  of  increasing  the  activity  of  the  gland  by  injection  of  secretin 
(Dale),  apparently  at  the  expense  of  the  proper  glandular  alveoli. 
The  degeneration  which  they  sometimes  undergo  in  cases  of  diabetes 


THE   PANCREAS. 


317 


mcllitus  seems  to  suggest  that  they  are  concerned  with  the  influence 
exerted  by  the  pancreas  on  the  metabolism  of  carbohydrates. 


Fig.  387— Section  of  pancreas  of  armadillo  showing  several  alveoli 
AND  A  large  interalveolar  CELL-ISLET.     (V.   D.   Harris.) 

The  cells  of  the  alveoli  are  shruukeii,  but  they  show  markedly  the  two  zones,  the  outer 
or  nou-graiuilar  stained  deeply  by  haematoxj-lin. 

The  cells  which  line  the  alveoli  are  columnar  or  polyhedral  in  shape. 
When  examined  in  the  fresh  condition,  or  in  sections  stained  by 
certain  methods,  their  protoplasm  is  seen  to  be  filled  in  the  inner 
two-thirds    with    granules,    but    the    outer    third    is    left    clear    or;  is 


Fig.  388. — Injection  of  blood-vessels  of  an  "islet"  of  the  pancreas. 
(Kiibne  and  Lea.) 


Striated  (fig.  390,  A  :  fig.  386).  After  a  period  of  activity  the  clear 
part  of  the  cell  becomes  larger,  and  the  granular  part  smaller 
(fig.  390,  B).  In  hccmatoxylin-stained  sections  the  outer  part  is 
coloured  more  deeply  than  the  inner  (fig.  387). 


318 


THE   ESSENTIALS   OF   HISTOLOGY. 


Pancreas  cells  frequently  exhibit  a  rounded  mass  of  granxiles  or 
fibrils  (mitochondria)  near  the  nucleus,  which  is  known  as  the  para- 
nucleus (Nebenkern) :  this  is  probably  related  to  the  secretory  activity 
of  the  cells  (see  p.  5). 


Fig.  389. — From  a  section  of  human  pancreas,     (v.  Ebner.)    Magnified 
530  diameters. 
a,  a,  outer  zones  of  alveolar  cells  witli  striated  appearance ;   h,  inner  granular  zones ; 
))i,    rnembrana   propria ;    c,   centro-acinar  cells,   here   occurring  in   unusuall}'   large 
amount;   d,  junctional  part  of  duct;  its  epithelium  is  continuous  with  the  centro- 
acinar  cells. 

In  the  centre  of  each  acinus  there  may  generally  be  seen  some 
spindle-shaped  cells  {centro-acinar  cells  of  Langerhans — fig.  386,  (/),  the 
nature  of  which  has  not  been  definitely  determined  ;  but  they  appear  to 
be  continued  from  the  cells  which  line  the  smallest  ducts  (fig.  386,  e) 


Fig.  390. — Part  of  an  alveolus  of  the  rabbit's  pancreas.     A,  at  rest; 
B,  after  active  secretion.     (From  Foster,  after  Kiihne  and  Lea.) 

a,  the  inner  granular  zone,  which  in  A  is  larger  and  more  closely  studded  with  fine 
granules  than  in  B,  in  which  the  granules  are  fewer  and  coarser;  h,  the  outer  trans- 
parent zone,  small  in  A,  larger  in  B,  and  in  the  latter  marked  witli  faint  striae  ;  c,  the 
lumen,  very  obvious  in  B,  but  indistinct  hi  A  ;  d,  au  indentation  at  the  junction  of 
two  cells,  only  distinct  in  B. 

Sometimes  they  are  much  more  conspicuous  and  fill  the  parts  of  the 
alveoli  which  are  nearest  to  the  duct  (fig.  389) ;  in  these  cases  the  mass 
of  cells  which  they  form  is  liable  to  be  mistaken  for  a  Langerhans'  islet. 


THE   PANCREAS. 


319 


Diverticula  from  the  lumen  of  the  alveolus  penetrate  between  the 
alveolar  cells  (tii;-.  'M)\),  as  in  the  salivary  glands  (j).  'JSfj).  The  pancreas 
has  many  nerves,  with   numerous  small  nerve-cells  distributed  upon 


Fig.  391. — A  duct  of  thk  pancreas  with  lateral  diverticula  into  the 
alveoli;  golgi  method.     (E.  Miiller.) 

In  A  the  duot  i.s  shown  out  longitudinally  and  giving  off  ductules,  m,  to  the  alveoli, 
where  they  extend  between  the  cells  (0-  In  B  the  details  of  their  termination  are 
shown  more  highly  magnified. 

their  course  ;  the  nerve-fibrils  end  by  ramifying  amongst  the  cells  of 
the  alveoli,  as  in  the  salivary  glands.  In  the  cat,  which  has  Pacinian 
bodies  in  its  mesentery,  these  terminal  organs  are  also  found  numer- 
ously in  the  substance  of  the  pancreas  (V.  D.  Harris). 


320  THE   ESSENTIALS  OF   HISTOLOGY. 


LESSON    XXXVI. 

STRUCTURE  OF  THE  KIDNEY. 

\.  Sections  passing  thiough  the  whole  kidney  of  a  small  mammal,  such  as  a 
mouse  or  rat.  These  sections  will  show  the  general  arrangement  of  the  organ 
and  the  disposition  of  the  tubules  and  of  tlie  Malpighian  corpuscles. 

2.  Thin  sections  of  the  kidney  of  a  larger  mammal,  such  as  the  dog  or  cat, 
may  next  be  studied.  In  some  the  direction  of  the  section  should  be  parallel 
with  the  rays  of  the  medulla,  and  in  others  acro.ss  their  direction.  The 
characters  of  the  epithelium  of  the  sevend  parts  of  the  uriniferous  tubules 
and  the  structure  of  the  glomeruli  are  to  be  made  out  in  these  sections. 

3.  Separate  portions  of  the  in-iniferous  tubules  may  be  studied  in  teased 
preparations  from  a  kidney  which  has  been  macerated  in  diluted  hydro- 
chloric acid  (1  to  .')  water).  This  renders  it  possible  to  unravel  the 
uriniferons  tubules  for  some  distance. 

4.  Thick  sections  of  a  kidney  in  which  the  blood-vessels  have  been 
injected.  Examine  these  with  a  low  power  of  the  microscope.  Follow  the 
course  of  the  arteries — those  to  the  cortex  sending  their  branches  to  the 
glomeruli,  those  to  the  medulla  rapidly  dividing  into  pencils  of  fine  vessels 
which  run  between  the  straight  uriniferons  tubules  of  the  boundary  zone. 
Notice  also  the  efferent  vessels  from  the  glomeruli  breaking  up  into  the 
capillaries  which  are  distributed  to  the  tubules  of  the  cortical  substance. 


The  kidney  is  a  compound  tubular  gland.  To  the  naked  eye  it 
appears  formed  of  two  portions — a  cortical  and  a  mechdlary.  The  latter 
is  subdivided  into  a  number  of  pyramidal  portions  {pyramids  of 
Malpighi),  the  base  (boundary  zone)  of  each  being  surrounded  by 
cortical  substance,  while  the  apex  projects  in  the  form  of  a  papilla  into 
the  dilated  commencement  of  the  ureter  (pelvis  of  the  kidney).^  Both 
cortex  and  medulla  are  composed  entirely  of  tubules — the  uriniferons 
tubules — which  have  a  straight  direction  in  the  medulla  and  a 
contorted  arrangement  in  the  cortex ;  but  groups  of  straight  tubules 
also  pass  from  the  medulla  through  the  thickness  of  the  cortex 
(medullary  rays). 

The  uriniferous  tubules  begin  in  the  cortical  part  of  the  organ  in 
dilatations,  each  inclosing  a  tuft  or  glomerulus  of  convoluted  capillary 
blood-vessels  (corpuscles  of  Malpighi),  the  dilated  commencement  of  the 
tubule  being  known  as  the  capsule  (fig.   396,    1).      The  glomerulus  is 

1  In  many  animals  (e.g.  dog,  cat,  rabbit,  most  monkeys)  the  whole  kidney  is 
formed  of  only  a  single  pyramid,  but  in  man  there  are  about  twelve. 


UKINIFEKOUS   TUBULES. 


321 


lobulated  (figs.  394,  395) ;    the  lobules  being  united  by  the  afferent 
and  efferent  vessels  and  covered  by  a  syncytium  reflected  from  the 


Fig.   392.— Diagram  of  the  course  of  the  tubules  in  a  uxipyramidal 

KIDXET,    such    as    THAT    OF    THE    RABBIT.       (Toldt.) 

'I,  Malpighian  bodies  ;  h,  first  convoluted  tubule  ;  c,  d,  looped  tube  of  Henle  ;  e,  second 
convoluted  ;  f,  collecting  tube  ;  g,  ducts  of  Bellini. 


Fig. 


393.— Section    through    part    of 

DOG'S   KIDNEY.       (Ludwig. ) 


p,  papillarj',  and  g,  boundary  zones  of  the  medulla  ; 
/-,  cortical  layer;  h,  bundles  of  tubules  in  the 
boundary  layer,  separated  by  spaces,  6,  containing 
bunches  of  vessels  (not  here  represented),  and 
prolonged  into  the  cortex  as  the  medullary  rays, 
III ;  c,  intervals  of  cortex,  composed  chiefly  of  con- 
voluted tubules,  with  irregular  rows  of  glomeruli, 
between  the  medullary  rays. 


epithelium  lining  the  capsule.  The  glomeruli  near  the  medulla  are 
larger  than  the  rest  and  have  more  lobules.  The  capillary-wall  in  all 
the  glomeruli  is  a  syncytium,  showing  no  cell-outlines  in  silver  pre- 
parations (Drasch). 


L 


322 


THE   ESSENTIALS   OF   HISTOLOGY. 


The  tubule  leaves  the  capsule  by  a  neck  (2),  which  is  rarely  narrower 
than  the  rest  of  the  tubule  in  mammals,  but  in  some  animals  (e.r/.  frog) 


Fig.   394.— a  malpighian  corpu.scle  from  the    kidney    of   the   momkey. 
(Szj-monowicz.)     Magnified  3-50  diameters. 

ft,  a,  sections  of  convoluted  tubules  ;  «',  comniencenient  of  convoluted  tube  from  capsule 
b,  capsule  ;  c,  afferent  and  efferent  vessels  of  glomerulus. 


Fig.  395. — Model  of  a  glomerulus.     (Johnson. 
a,  afferent ;  c,  efferent  blood-vessel. 


URINIFEROUS  TUBULES. 


323 


is  long,  and  has  ciliated  epithelium  ;  the  tubule  is  at  first  convoluted 
(first  convolaled  tubule,  3),  but  soon  becomes  nearly  straight  or  slightly 
spiral  only  {spiral  tuhuU;  4),  and  then,  rapidly  narrowing,  passes  down 


Fig.  39fi.— Diagram  of  the  course  of  two  urixiferous  tubules.     (Klein.) 

A,  cortex  ;  B,  boundary  zone  ;  c,  papillary  zone  of  the  medulla  ;  a,  a',  superficial  and  deep 
layers  of  cortex,  free  from  glomeruli.  For  the  explanation  of  the  numerals,  see  the 
text. 


into  the  medulla  towards  the  dilated  commencement  of  the  ureter  as 
the  desrendinrt  tubule  of  Henle  (5).  It  does  not  at  once,  however,  open 
into  the  pelvis  of  the  kidney,   but  before  reaching  the  end    of  the 


324  THE   ESSENTIALS   OF   HISTOLOGY. 

papilla  it  turns  round  in  the  form  of  a  loop  {hop  of  Henle,  6)  and  passes 
upwards  again  towards  the  cortex,  parallel  to  its  former  course,  and  at 
first  somewhat  larger  than  before,  but  afterwards  diminishing  in  size 
{ascending  tubule  of  Henle,  7,  8,  9).  Arrived  at  the  cortex  it  approaches 
close  to  the  capsule  from  which  the  tubule  took  origin,  but  at  a  point 
opposite  to  the  origin,  viz.  near  the  afferent  and  eft'erent  vessels  of  the 
glomerulus  (Golgi).  It  then  becomes  larger  and  irregularly  zigzag 
{zigzag  or  irregular  tubule,  10),  and  may  again  be  somewhat  convoluted 
(second  convoluted  tubule,  11),  eventually,  however,  narj-owing  into  a 
small  vessel  {junctional  tubide,  12),  which  joins  a  straight  or  collecting 
tubule  (13).     The  last-named  unites  Avith  others  to  form  large  collecting 

tubes  which  pass  through  the  medul- 
^■---^  lary  substance  of  the  kidney  (14)  to 

open  at  the  apex  of  the  papilla  as  the 
ducts  of  Bellini  (15). 

The  tubules  are  throughout  bounded 
k  by    a    basement-membrane,    which    is 

fc_        ■  lined  b}'  epithelium,  but  the  characters 

W:J.  of   the    epithelium  cells    vary   in    the 

^' •  different   parts  of  a  tubule.      In   the 

capsule  the  epithelium  is  flattened  and 

""    '■■■*"■'"' — i-^— -^  is  reflected  over  the  glomerulus.     In 

Fig.  397.— Section-  of  a  coNvoLrTED     some  animals  {e.g.  mouse)  the  granular 

TUBULE  OF  THE  RABBITS  KiDXET,     epithclium  of  the  couvoluted  tube  is 

SHOWING     THE     STRUCTURE    OF    THE  ^ 

EPITHELIUM.  (Szymonowicz.)  (Mag-     prolonged  a  little  way  into  the  capsule. 

nified  1100  diameters.)  t^t."!^^  7jj         i        ■     i  i    i    i 

In  the  nrst  convolutect  and  spiral  tubules 
the  epithelium  is  thick,  and  the  cells  are  markedly  granular,  with  a 
tendency  for  the  granules  to  be  arranged  in  lines  perpendicular  to  the 
basement-membrane  (rodded  or  fibrillar  appearance,  fig.  397).  The 
granules  of  the  cells  are  particularh'^  well  displaved  in  sections  stained 
by  Muir's  method ;  they  are  eosinophil,  like  the  granules  of  secreting 
cells  generally.  They  often  exhibit  a  brush  of  cilium-like  processes 
projecting  into  the  lumen  (figs.  397,  400),  but  these  are  not  vibratile 
in  mammals.  In  the  narrow  descending  limb  of  the  looped  tubules, 
and  in  the  loop  itself,  the  cells  are  clear  and  flattened  and  leave 
a  relatively  large  lumen ;  in  the  ascending  limb  they  again  acquire  a 
granular  structure  and  may  nearly  fill  the  lumen.  The  arrangement 
of  the  cell-granules  in  lines  perpendicular  to  the  basement-membrane 
is  still  more  marked  in  the  zigzag  tubides,  and  a  similar  structure 
is  present  also  in  the  second  convoluted  tubules,  into  which  these  pass. 
On  the  other  hand,  the  junctional  tidtule  has  a  large  lumen  and  is 
lined  by  clear  flattened  cells,  and  the  collecting  tubes  have  also  a  very 


URINIFEROUS  TUBULES. 


325 


distinct  lumen  and  are  lined  by  a  clear  cubical  or  columnar  epithelium 
(tiff.  398,  a). 


Fig.  .398.— Section  across  a  papilla  of  the  kidney.     (Cadiat.) 
a,  large  collectiug  tubes  (ducts  of  Bellini) ;  h,  c,  d,  tubules  of  Henle  ;  e,  .r,  blood-capillaries. 

The  following  gives  a  tabular  view  of  the  parts  which  compose  a 
uriniferous  tubule,  and  the  nature  of  the  epithelium  in  each  part : — 


Portion  of  TuBrLE. 


Xatlre  of  Epithelium. 


Position  of  Tubcle. 


Capsule 

First  convoluted  tube    . 

Spiral  tube    . 

Small     or     descending  i 
tube  of  Henle    .         .   ■ 


Flattened,  reflected  over  glomerulus, 
where  its  cells  form  a  syncytium. 

Cubical,  granular,  with  appearance 
of  fibrillation  ("redded '"),  the  cells 
interlocking    ..... 

Like  the  last      ..... 

Clear  flattened  cells  .... 


Loop  of  Henle 

Larger     or      ascending 

tube  of  Henle    . 
Zigzag  tube   . 

Second  convoluted  tube 


Junctional  tube     . 

Straight    or    collecting 
tube  .... 
Duct  of  Bellini 


Like  the  last 


Cubical,  granular  :  the  cells  some- 
times imbricated     .... 

Cells  strongly  '"  rodded  '"' :  varying 
height,  lumen  small 

Similar  to  first  convoluted  tube,  but 
cells  are  longer,  with  larger  nuclei, 
and  they  have  a  more  refractive 
aspect     ...... 

Clear  flattened  and  cubical  cells 

Clear  cubical  and  columnar  cells 
Clear  columnar  cells  .... 


Labyrinth  of  cortex.^ 

Labyrinth  of  cortex. 

Medullary  ray  of 
cortex. 

Boundary  zone  and 
partly  papillary 
zone  of  medulla. 

Papillary  zone  of 
medulla. 

Medulla,  and  medul- 
lary ray  of  cortex. 

Labyrinth  of  cortex. 

Labyrinth  of  cortex. 


Labyrinth  passing  to 

medullars  ray. 
Medullary   ray   and 
medulla. 
I  Opens    at    apex    of 
I       papilla. 


1  The  part  of  the  cortex  between  and  surrounding  the  medullary  rays  is  so  named. 


326  THE   ESSENTIALS   OF   HISTOLOGY. 

Blood-vessels. — The  renal  artery  divides  into  branches  on  entering 
the  organ,  and  these  branches  pass  towards  the  cortex,  forming 
incomplete  arches  between  the  cortex  and  the  medulla  (fig.  399,  a). 
The    branches   of    the   renal   vein   form   similar   but    more   complete 


Fig.  399. — Vascular  supply  of  kidney.  '  (Cadiat.)    Diagrammatic, 
a,  part  of  arterial  arch ;  6,  interlobular  artery  ;  c,  glomerulus  ;  d,  efferent  vessel  passing 
to  medulla  as  false  arteria  recta  ;   e,  capillaries  of  cortex  ;  /,  capillaries  of  medulla ; 
g,  venous  arch  ;  h,  straight  veins  of  medulla  ;  j,  vena  stellula  ;  i,  interlobular  vein. 

arches  (g). — From  the  arterial  arches  vessels  pass  through  the  cortex 
(cortical  oi-  interlobular  arteries,  b),  and  give  off  at  intervals  small  arteri 
oles  (afferent  vessels  of  the  gl'>meruli),  each  of  which  enters  the  dilated 
commencement  of  a  uriniferous  tubule,  within  which  its  capillaries  form 
a  glomerulus.  From  the  glomerulus  a  somewhat  smaller  efferent  vessel 
passes  out,  and  this  at  once  again  breaks  up  into  capillaries,  which  are 


BLOOD-VESSELS   OF   KIDNEY. 


827 


distributed  amongst  the  tubules  of  the  cortex  (e) ;  their  blood  is 
collected  by  veins  which  run  parallel  with  the  cortical  arteries  but 
not  in  juxtaposition  with  them  :  these  veins  join  the  venous  arches 
between  the  cortex  and  the  medulla ;  they  receive  blood  from  certain 
other  veins  Avhich  arise  by  radicles  having  a  somewhat  stellate  arrange- 
ment near  the  capsule  {vence  dellvlce,  j). 

The  medulla  derives  its  blood-supply  from  special  offsets  of  the 
arterial  arches,  which  almost  immediately  break  up  into  pencils  of 
fine  straight  arterioles  running  in  groups  between  the  straight  tubules 
of  the  medulla.      These  arterioles   supply  a  capillary  network  with 


Fig.    400. — Nerve    fibrils    ending    over    capillary    blood-vessels    and 

AMONGST   THE    EPITHELIUM    CELLS   OF   A   CONVOLUTED   TUBE    OF    THE    FROG'S 

KIDNEY.     (Smirnow.) 

elongated  meshes  which  pervades  the  medulla  (fig.  399,/),  and  which 
terminates  in  a  plexus  of  somewhat  larger  venous  capillaries  in  the 
papillce.  From  these  and  from  the  other  capillaries  the  venules  of 
the  medulla  collect  the  blood,  and  pass,  accompanying  the  straight 
arterioles,  into  the  venous  arches  between  the  cortex  and  medulla.  The 
groups  of  small  arteries  and  veins  (rasn  recta)  in  the  part  of  the  medulla 
nearest  to  the  cortex  alternate  with  groups  of  the  uriniferous  tubules, 
and  this  arrangement  confers  a  striated  aspect  upon  this  portion  of  the 
medulla  {houndanj  zone,  fig.  39-3,  g). 

The  efferent  vessels  of  those  glomeruli  which  are  situated  nearest 
to  the  medulla  also  break  up  into  pencils  of  fine  vessels  {false  vasa 
recta)  which  join  the  capillary  network  of  the  medulla  (fig.  399,  (/). 

Between  the  uriniferous  tubules,  and  supporting  the  blood-vessels, 
is  a  certain  amount  of  connective  tissue  (fig.  400),  within  which  are 
cleft-like  h'mphatics. 

Nerve-fibrils  are  described  as  ramifying  amongst  the  epithelium-cells 
of  the  tubules  (fig.  400),  but  most  of  the  nerves  to  the  kidneys  are 
distributed  to  the  blood-vessels. 


328  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    XXXVII. 

STRUCTURE  OF  THE   URETER,   BLADDER,   AND 
MALE  GENERATIVE  ORGANS. 

1.  Section  across  the  lower  part  of  the  ureter.     Another  section  may  be 
taken  across  the  upper  part  near  the  pelvis  of  the  kidney. 

2.  Section  of  the  urinaiy  bladder  vertical  to  the  surface. 

In  the  sections  of  the  ureter  and  of  the  urinary  bladder,  notice  the  tran- 
sitional epithelium  resting  on  a  raucous  membrane,  which  is  composed  of 
areolar  tissue  without  glands  (in  most  animals),  and  the  muscular  coat 
outside  this.  In  the  ureter  there  is  a  layer  of  connective  tissue  outside  the 
muscular  coat,  and  at  the  upper  part  of  the  bladder  a  layer  of  serous 
membrane  covering  the  muscular  tissue. 

3.  Section  across  the  penis  (child  or  monkey).  The  blood-vessels  of  the 
organ  should  be  injected  with  the  hardening  fluid  .so  as  the  better  to  exhibit 
the  arrangement  of  the  venous  spaces  which  constitute  the  erectile  tissue. 
Notice  the  large  venous  sinuses  of  the  corpora  cavernosa  and  the  smaller 
spaces  of  the  corpus  spongiosum,  in  the  middle  of  which  is  seen  the 
(flattened)  tube  of  the  urethra. 

4.  Section  across  urethra  and  ])rostate  gland  (child  or  monkey).  Notice 
the  glandular  tubes  and  the  plain  muscular  tissue  of  the  prostate,  and  the 
character  of  the  urethral  epithelium. 

5.  Section  of  testis  and  epididymis.  The  sections  may  be  made  from 
a  rat's  testis  which  has  been  hardened  in  alcohol  ;  they  can  be  stained 
with  iron-hsematoxylin.  In  these  sections  notice  the  strong  capsule  sur- 
rounding the  gland,  the  substance  of  which  consi.sts  of  tubules  which  are 
variously  cut  ;  and  the  epithelium  of  the  tubules,  which  is  in  different 
phases  of  development  in  different  tubules.  Observe  the  strands  of  poly- 
hedral interstitial  cells,  much  more  numerous  in  some  animals,  lying  in  the 
loose  tissue  between  the  tubules  ;  also  the  lymphatic  clefts  in  that  tissue. 
Notice  in  sections  through  the  epididymis  the  epithelium  of  that  tube. 

Sketch  carefully  under  a  high  power  the  contents  of  some  of  the  semini- 
ferous tubules  to  illustrate  the  mode  of  formation  of  the  spermatozoa. 

6.  Examination  of  spermatozoa.  Spermatozoa  may  be  obtained  fresh  from 
the  testicle  or  seminal  vesicles  of  a  recently  killed  mammal  and  examined  in 
saline  solution.  Their  movements  may  be  studied  on  the  warm  stage  ;  to 
display  their  structure  a  very  high  power  of  the  microscope  is  necessary. 
They  mav  be  preserved  and  stained  as  "  fllm  "  pi'eparations,  as  with  marrow 
(P-30).     "  

The  ureter  (fig.  401)  is  a  muscular  tube  litied  by  mucous  membrane. 
The  muscular  coat  consists  of  two  layers  of  plain  muscular  tissue,  an 
outer  circular,  and  an  inner  longitudinal.  In  the  lower  part  there 
are  some  longitudinal  bundles  external  to  the  circular.  Outside  the 
muscular  coat  is  a  layer  of  connective  tissue  in  which  the  blood-vessels 
and  nerves  ramify  before  entering  the  muscular  layer. 


THE   BLADDER. 


329 


The  mucous  membrane  is  composed  of  areolar  tissue  and  is  lined  by 
transitional  epithelium  (fig.  402). 

The  urinary  bladder  has  a  muscular  wall  lined  by  a  strong  mucous 
membrane  and  covered  in  part  by  a  serous  coat. 


*i>.. 


i'£. 


gn-ia&JEK^ 


i)   e"^<iB>' 


l^^#% 


SF%> 


%, 

^.i^'>: 


^ill^ 


%  ig?--.i 


Fig.  401. — Section  across  the  upper  part  of  the  oketer.     (v.  Ebner.) 

Magnified  14  diameters. 

e,  epithelium  ;  «,  mucous  membrane ;  I,  longitudinal  muscle  ;  r,  circular  mu.scle. 


Jio."^" 


-.--  d 


Fig.  402.  —Section  of  the  mucocs  jieiibrane  of  the  bladder  to  show  its 
epitheliuji.      (Sz\-monowicz. ) 
a,  h,  superficial  epithelium-cells  ;  c,  leucocyte  ;  d,  areolar  tissue  of  mucous  membrane. 

The  muscular  coat  consists  of  three  layers,  but  the  innermost  is 
incomplete.  The  principal  fibres  run  longitudinally  and  circularly, 
and  the  circular  fibres  are  collected  into  a  layer  of  some  thickness  which 
immediately  surrounds  the  commencement  of  the  urethra.  The  mucous 
membrane  is  lined  by  a  transitional  stratified  epithelium  like  that  of 


330 


THE    ESSENTIALS   OF   HISTOLOGY. 


the  ureter.  The  shape  and  structure  of  the  cells  have  already  been 
studied  (p.  5.5).     Many  of  the  superficial  cells  have  two  nuclei. 

The  nerves  to  the  bladder  form  gangliated  plexuses,  and  are  dis- 
tributed to  the  muscular  tissue  and  blood-vessels,  but  some  are  said  to 
enter  the  epithelium. 

The  penis  is  mainly  composed  of  cavernous  tissue  which  is  collected 
into  two  principal  tracts — the  corpora  cavernosa,  one  on  each  side,  and 
the  corpus  spongiosum  in  the  middle  line  inferiorly.  All  these  are 
bounded  by  a  strong  capsule  of  fibrous  and  plain  muscular  tissue,  con- 
taining also  many  elastic  fibres  and  sending  in  strong  septa  or  trabeculse 


Fig.  403.— Section  of  erectile  tissue.     (Cadiat.) 

a,  trabeculse  of  connective  tissue,  with  elastic  fibres,  and  bundles  of  plain  muscular 

tissue,  some  cut  across  (c) ;  6,  venous  spaces. 


of  the  same  tissues,  which  form  the  boundaries  of  the  cavernous  spaces 
of  the  erectile  tissue  (fig.  403).  The  arteries  of  the  tissue  run  in  these 
trabeculse,  and  their  capillaries  open  into  the  cavernous  spaces.  On 
the  other  hand,  the  spaces  are  connected  with  eflferent  veins.  The 
arteries  of  the  cavernous  tissue  may  sometimes  in  injected  specimens 
be  observed  to  form  looped  or  twisted  projections  into  the  cavernous 
spaces  {helicine  arteries  of  MuUer),  into  which  they  may  open  directly. 

The  integument  of  the  penis  and  clitoris,  especially  that  of  the 
glans,  contains  numerous  special  nerve  end  organs  of  the  nature  of  end- 
bulbs  (see  p.  169),  and  Pacinian  bodies  are  also  found  upon  the  nerves. 
Lymphatic  vessels  are  numerous  in  the  integument  of  the  organ  and 
also  in  the  submucous  tissue  of  the  urethra. 


THE    URETHRA.  331 

Urethra.— The  cross-section  of  the  urethra  appears  in  the  midHle 
of  the  corpus  spongiosum  in  the  form  of  a  transverse  cleft.  It  is  lined 
in  the  prostatic  part  by  transitional,  but  elsewhere  by  columnar 
epithelium,  except  near  its  orifice,  where  the  epithelium  is  stratified. 
In  the  female  urethra  it  is  stratified  throughout.  The  epithelium  rest? 
upon  a  vascular  mucous  membrane,  which  contains  longitudinally 
disposed  plain  muscular  fibres,  and  in  the  membranous  urethra,  cir- 
cularly disposed  cross-striated  fibres.  Outside  the  mucous  membrane 
is  a  coating  of  submucous  tissue,  with  two  layers  of  plain  muscular 
fibre — an  inner  longitudinal  and  an  outer  circular.     Outside  this  again 


'■<£^_ 


Fig.   404. — Seciiox  of  prostate.     (Heitzmann.) 
il,  muscular  tissue  ;  E,  epithelium  ;  C,  concretions. 

is  a  close  plexus  of  small  veins  which  is  connected  with,  and  may  be 
said  to  form  part  of,  the  corpus  spongiosum. 

The  mucous  membrane  of  the  urethra  is  beset  with  small  mucous 
glands,  simple  and  compound  (glands  of  Littre).  There  are  also  a 
number  of  oblique  recesses  termed  lacunce.  Besides  these  small  glands 
and  glandular  recesses,  two  compound  racemose  glands  open  into  the 
bulbous  portion  of  the  nrethra  (Cowpers  glands).  Their  acini  are  lined 
by  clear  columnar  cells  which  yield  a  mucus-like  secretion. 

The  prostate,  which  surrounds  the  commencement  of  the  urethra,  is 
a  muscular  and  glandular  mass,  the  glands  of  which  are  composed  of 
tubular  alveoli,  lined  by  columnar  epithelium,  with  smaller  cells  h'ing 
between  them  and  the  basement-membrane   (fig.  404).     Their  ducts 


332  THE   ESSENTIALS   OF   HISTOLOGY. 

open  upon  the  floor  of  the  urethra.  In  old  subjects  the  tubules  often 
contain  colloid  or  calcareous  concretions.  The  muscular  tissue  is  of 
the  plain  variety. 

Blood-vessels  and  nerves  are  numerous.  The  nerves  are  provided 
with  small  ganglia  and  are  distributed  partly  to  the  muscular  tissue, 
partly  to  the  glands,  and  others  (sensory)  to  the  capsule,  and  to  the 
wall  of  the  urethra.  The  sensory  nerves  end  in  plexuses  and  in  peculiar 
terminal  corpuscles  like  simple  Pacinian  bodies  (Timofeew). 

a  h 


Fig.  405. — Sectio.\  of  humax  testis  and  epididymis,  somewhat  magnified. 
(Bohm  and  v.   Davidoff.) 

a,  glandular  substance  divided  into  lobules  by  septa  of  connective  tissue  ;  b,  tunica  albu- 
ginea  ;  c,  head  of  epididymis  ;  d,  rete  testis  ;  c,  middle  part  or  body  of  epididymis  ;  /, 
mediastinum  giving  oi-igin  to  the  septa ;  rj,  sections  of  the  commencing  vas  deferens. 

The  testicle  is  inclosed  by  a  strong  fibrous  capsule,  the  tunica 
alhug'mea  (tig.  405,  h).  This  is  covered  externally  with  a  layer  of  serous 
epithelium  reflected  from  the  tunica  vaginalis.  From  its  inner  surface 
there  proceed  fibrous  processes  or  tmhecuke,  which  imperfectly  subdivide 
the  organ  into  lobules,  and  posteriorly  the  capsule  is  prolonged  into  the 
interior  of  the  gland  in  the  form  of  a  mass  of  fibrous  tissue,  which  is 
known  as  the  mediastimm.  testis  (fig.  405,  /).  Attached  to  the  posterior 
margin  of  the  body  of  the  gland  is  a  mass  (epididymis)  which  when 
investigated  is  found  to  consist  of  a  single  convoluted  tube,  receiving  at 


THE   TESTICLE. 


333 


its  upper  end  the  rj/nrnf  ducts  of  the  testis  and  prolonged  at  its  lower 
end  into  a  thick-walled  nniscidai'  tube,  the  vas  deferens,  which  conducts 
the  secretion  to  the  urethra. 

The  glandular  substance  of  the  testicle  is  wholly  made  up  of 
canvoluted  tubules,  which  wlien  unra\elled  are  of  very  considerable 
length.  Each  commences  near  the  tunica  albuginea,  and  after  many 
windings   terminates,   usually  after   joining  one  or  two  others,    in  a 


Fig.  406. — Passage  of  convoluted   seminu-'erous  tubules  into  straight 

TUBULES    AND   OF   THESE   INTO   THE   RETK   TESTIS.       (Mihalkowicz. ) 

(1,  seminiferous  tubules ;    6,   fibrous   stroma  continued   from   the   mediastinum   testis ; 

c,  rete  testis. 


straight  tubule,  which  passes  into  the  mediastinum,  and  there  forms, 
by  uniting  with  the  other  straight  tubules,  a  network  of  intercom- 
municating vessels  of  varying  size,  which  is  known  as  the  rete  testis 
(fig.  406).  From  the  rete  a  certain  number  of  efferent  tubules  arise, 
and  after  a  few  convolutions  pass  into  the  tube  of  the  epididymis. 

The  straight  tubules  which  lead  from  the  convoluted  seminiferous 
tubes  into  the  rete  testis  are  lined  only  by  a  single  layer  of  clear 
flattened  or  cubical  epithelium.     The  tubules  of  the  rete  also  have  a 


334  THE   ESSENTIALS   OF   HISTOLOGY. 

simple  epithelial  lining;  both  in  these  and  in  the  straight  tubules  the 
basement-membrane  is  absent,  the  epithelium  being  supported  directly 
by  the  connective  tissue  of  the  mediastinum. 

The  efferent  tubules  which  pass  from  the  rete  to  the  epididymis  are 
lined  by  columnar  ciliated  epithelium  In  man  their  lumen  is  irregular 
in  section,  and  the  inner  surface  pitted  with  depressions  (intra-epithelial 
glands)  lined  by  short  clear  non-ciliated  cells  (J.  Schaffer).  The  tube 
of  the  epididymis  is  lined  by  long  columnar  cells  having  at  their  bases 


,'y^ 


a 


5? J  I    \il\ 


Fig.   407. — Section  of  the  TinK  oi'  the  epididymis.     (Szymonowicz.) 

(MagniHed  oUO  diameters.) 

(t,  blood-vessel  ;  b,  circular  muscular  fibres  ;  r,  epithelium. 

smaller  cubical  cells  with  spherical  nuclei  (fig.  407).  The  columnar  cells 
are  provided  with  what  appear  to  be  bunches  of  cilium-like  fibrils  pro- 
jecting into  the  lumen  of  the  tube.  These  apparent  cilia  are,  however, 
not  vibratile  as  was  formerly  supposed,  and  are  therefore  not  true  cilia 
(Neumann,  Myers-Ward).  They  appear  to  vary  in  development  in 
different  cells,  and  are  probably  connected  in  some  way  with  the 
formation  of  the  secretion  of  the  epididymis  and  its  extrusion  into 
the  lumen  of  the  tube.  The  epididymis  cells  exhibit  canaliculi  in 
their  cytoplasm,  which  according  to  Holmgren,  communicate  with  the 
exterior  at  the  attached  border  of  the  cell  (fig.  408).     The  tube  of 


THE   'rKSIMCLK. 


335 


the  epididymis  has  a  considerable  amount  of  |)laiii   iniiseulai-  tissue  in 
its  wall  (fig.  407). 

The  ras  deferens  (fig.  109)  is  a  thick-walled  tube,  formed  of  an  outer 


A!^A  '■'^^mk 


Fig.  408.— Cells  of  epididymis,  showing  canalization  of  the  cytoplasm. 
(E.  Holmgren.) 


Fig.  409.— Section  across  the  commencement  of  the  vas  deferens.    (Klein.) 
a,  epithelium  ;   b,  mucous  membrane  ;    c,  d,  e,  inner,  middle,  and  outer  layers  of  the 
muscular  coat ;  /,  bundles  of  the  internal  creniaster  muscle  ;  g,  section  of  a  blood- 
vessel. 

layer  of  longitudinal  bundles  of  plain  muscular  tissue;  within  this  an 
equally  thick  layer  of  circular  bundles  of  the  same  tissue,  and  within 
this  again  a  thinner  layer  of  longitudinal  muscle.  There  is  a  good  deal 
of  connective  and  elastic  tissue  between  the  muscular  bundles.     The 


336 


THE   ESSENTIALS   OF   HISTOLOGY. 


tube  is  lined  by  a  mucous  membrane,  the  inner  surface  of  which  is 
covered  by  columnar  non-ciliated  epithelium. 

The  ampullcB  of  the  vasa  deferentia,  and  the  vesiculce  seminales,  are  in 
structure  similar  to  the  vas  deferens,  but  their  corrugated  walls  are 
much  thinner  and  less  muscular. 

The  connective  tissue  between  the  tuljules  of  the  testis  is  of  very 
loose  texture,  and  contains  numerous  lymphatic  clefts,  which  form  an 
intercommunicating  system  of  commencing  lymphatic  vessels.  Lying 
in   this  intertubular  tissue  are  strands  of  polyhedral   epithelium-like 


Fig.  410. 


Fig.  411. 


Fig.  410. — Section  of  parts  of  three  semixiferous  tubules  of  the  rat. 
n,  with  the  spermatozoa  lea.st  advanced  in  development ;  6,  more  advanced ;  r,  containing 

fully  developed  spermatozoa.     Between  the  tubules  are  seen  strands  of  interstitial 

cells  with  blood-vessels  and  lymph-spaces. 

Fig.  411.— Human  spermatozoa.    J-^^.    (G.  Retzius.) 

1,  in  jirofile  ;  2,  viewed  on  the  flat ;  b,  head ;  c,  middle  jiiece ;  d,  tail;  e,  end-piece  of  the 
tail,  which  is  described  as  a  distinct  part  by  Retzius. 


cells  {interstitial  cells,  see  fig.  410)  of  a  yellowish  colour;  they  are  much 
more  abundant  in  some  species  of  animals  (cat,  boar)  than  in  others. 
They  accompan}'  the  blood-vessels  before  these  break  up  to  form 
the  capillary  networks  which  cover  the  walls  of  the  seminiferous 
tubules. 

The  interstitial  cells  contain  in  many  animals  yellowish-brown  fat- 
globules  (staining  with  osmic  acid);  and  also  sometimes  needle-shaped 
crystals  (proteid).  Similar  fatty  globules  may  occur  in  the  Sertoli 
cells  of  the  seminiferous  tubules  (see  above),  and  have  been  thought 
to  be  derived  from  those  of  the  interstitial  tissue. 


THE   SEMINIFEROUS  TUBULES. 


337 


Structure  of  the  tubules. — The  seminiferous  tubules  are  formed  of  a 
thick  basement-membrane,  and  contain  several  layers  of  epithelium- 
cells.     Of  these  Wers,  the  one  next  to  the  basement-membrane  is  a 


Fig.  4r2.— HcjrAX  spekmatozoa  ox  the  flat  and  in  profile.     (Bramman.) 

Those  on  the  right  still  show  protoplasm  adhering  to  them.     Only  the  commencement  of 
the  tail  is  represeutftd  in  the  two  which  are  shown  in  profile.      Magnified  2500  diameters. 


stratum  of  clear  cubical  cells  {spermatogonia  or  spermagons,  figs.  410, 414,  a), 
the  nuclei  of  which  for  the  most  part  exhibit  the  irregular  network 
which  is  characteristic  of  the  resting  condition,  but  in  certain  tubules 
show  indications  of  division.    Here  and  there  between  the  spermatogonia 


338 


THE   ESSENTIALS   OF   HISTOLOGY. 


some  of  the  lining  epithelium-cells  are  enlarged,  and  project  between 
the  more  internal  layers,  being  connected  with  groups  of  developing 
spermatozoa.  The.se  enlarged  cells  are  the  cells  of  Sertoli  (fig.  414,  ((^,  a"  ; 
fig.  417). 

Next  to  this  lining  epithelium  is  a  zone  of  larger  cells  (spermatocytes 
or  spermocytes,  fig.  414,  h),  the  nuclei  of  which  are  usualh^  in  some 
stage  of  hetero-  or  homo-typical  mitotic  division;  these  cells  may  be 
two  or  three  deep  (as  in  a,  fig.  410).  Next  to  them,  and  most 
internal,   are  to  be  seen  in  some  tubules  (fig.  410,  h  and  c)  a  large 


a 


(I 


d 


S 


9 


Fig.  413. — Different  forms  of  spermatozoa.     (From  Verworn.) 

a,  of  bat ;  6,  c,  of  frog  ;  t?,  of  finch ;  c,  of  ram  ;  /,  j/,  of  boar  ;  A,  of  a  jelly-fish ; 
i,  of  a  monkey  ;  ?,  of  crab  ;  k.  of  round- worm. 


number  of  small  protoplasmic  cells  with  simple  spherical 
nuclei  {spermatids  or  spermids,  fig.  414,  c).  In  other  tubules 
the  spermatids  are  elongated,  and  the  nucleus  is  at  one 
end,  and  in  others  again  these  elongated  cells  are  converted 
into  evident  spermatozoa,  which  lie  in  groups :  their  heads 
projecting  between  the  deeper  cells  and  connected  with  one  of  the 
Sertoli  cells  of  the  lining  epithelium,  and  their  tails  emerging  into 
the  lumen  of  the  tubule  (fig.  410,  b).  As  they  become  matured  they 
gradually  shift  altogether  towards  the  lumen,  where  they  eventually 
become  free  (c).  During  the  time  that  this  crop  of  spermatozoa  has 
been  forming,  another  set  of  spermocytes  has  been  produced  by  the 
division  of  the  spermogonia,  and  on  the  discharge  of  the  spermatozoa 
the  process  is  repeated  as  before  (see  diagram,  fig.  414). 

The  spermatozoa. — Each  spermatozoon  or  sperm  consists  of  three 
parts,  a  head,  a  middle  part  or  body,  and  a  long  tapering  and  vibra- 
tile  tail  (figs.  411,  412).  In  man  the  head  is  of  a  flattened  oval 
shape,  somewhat  more  flattened  anteriorly  :  in  some  animals  it  bears 
a  small  barb-like  projection  at  its  extremity,  but  this  appears  to  be 


THE   SPERMATOZOA. 


339 


Fig.  414.— Diagram  exhibiting  the  cycle  of  phases  of  spermogenesis 

(rat). 
o,  lining  epithelium-cells  or  spermatogonia,  seen  dividing  in  6  ;  a',  a",  Sertoli  cells  ; 
b,  spermatocytes,  with  skein-like  nuclear  filaments.  These  cells  are  seen  actively 
dividing  in  5.  c,  spermatids,  forming  an  in-egular  column  or  clump  in  6,  7,  8,  and  1, 
and  connected  to  an  enlarged  Sertoli  cell,  a',  of  the  lining  epithelium  in  2,  3,  4, 
and  5.  In  6,  7,  and  8  advanced  spermatozoa  of  one  crop  are  seen  between  columns 
of  spermatids  of  the  next  crop.  «',  parts  of  the  spermatids  which  disappear  when 
the  spermatozoa  are  fully  formed  ;  s,  seminal  granules. 


Fig.  41.5.— Spermatozoa  from  the  rat  in  different  stages  of  develop- 
ment.    (H.  H.  Brown.) 

1-6,  developing  spermatozoa  from  the  testicle  ;  7,  a  mature  spermatozoon  from  the  vas 
deferens.  The  remains  of  the  protoplasm  of  the  cell,  which  is  seen  in  6  still  adhering 
to  the  middle  piece  of  the  sijermatozoon  and  containing  a  number  of  chromatin 
granules,  appears  to  be  thrown  off  as  the  spermatozoon  matures. 


340 


THE   ESSENTIALS   OF   HISTOLOGY. 


absent  in  the  human  spermatozoon.  The  apical  part  is  covered  by 
a  cap  of  a  somewhat  different  appearance  from  the  rest — the  head-cap. 
The  jiiiddle-jyiece  is  in  man  short  and  cylindrical,  and  has  a  spiral  fibre 
passing  round  it.  An  axial  fibre,  itself  fibrillated,  passes  from  a  knob 
close  to  the  head  right  through  the  body  and  tail.  The  tail  is  the 
longest  part  of  the  spermatozoon,  and  when  examined  with  the  micro- 
scope in  the  fresh  condition  is  seen  to  be  in  continual  vibratile  motion, 
the  action  resembling  that  of  a  cilium.  The  extremity  of  the  tail 
{end-piece)  forms  a  distinct  part  of  the   spermatozoon,   and  in  some 


10^ 


s 


Fig.   416. — Changes  in  the  spermatids  in  the  course  of  form.\tion  ok 

THE  SPERMATOZOA.      (Niessing.) 
The  tail  filament  is  seen  (iu  a  and  e)  to  extend  from  the  centrosome,  which  lies  close  to  the 

nucleus.     The  head-cap  (.shown  in  c)is  produced  by  a  transformation  of  part  of  the 

archoplasm  which  becomes  vacuolated  (6,  c,  (0- 

animals  may  split  into  two  or  three  fibrils ;  these  can  also  sometimes 
be  traced  along  the  whole  length  of  the  tail.  Human  spermatozoa 
are  about  0*05  mm.  (^i^  inch)  long,  the  head  and  middle-piece  each 
measuring  about  yV^^  ^^  ^^^^  amount. 

In  diff'erent  animals  the  shape  of  the  head  and  the  extent  of  middle- 
piece  and  tail  vary  greatly  (fig.  413).  In  the  rat  (fig.  415,  7)  the  head 
is  long,  and  is  recurved  anteriorly  ;  it  is  set  obliquely  on  the  middle- 
piece,  which  is  also  of  considerable  extent,  and  which  has  a  closely 
wound  spiral  filament  encircling  it  (H.  H.  Brown).  In  the  newt  the 
head  is  long  and  tapering,  and  the  tail  has  a  membranous  expansion, 
attached  in  a  spiral  manner  along  its  whole  length.     This  has  also  been 


SPERMOGENESIS.  341 

described  in  the  human  spermatozoon,  but  its  existence  here  is  doubt- 
ful. In  decapods,  which  possess  no  cilia,  the  spermatozoa  are  stellate 
and  motionless  (fig.  413,  /) ;  in  nematoid  worms  they  are  amoelioid 
(fig.  413,^-).  Sometimes  two  distinct  kinds  of  spermatozoa  are  met 
with  in  the  same  species  of  animal,  one  kind  being  far  the  larger  in  size 
(giant  spermatozoa)  but  much  less  numerous.  Such  giant  spermatozoa 
have  been  observed  in  man. 

Although  the  tail  of  the  spermatozoon  is  usually  classed  with  cilia, 
it  is  obvious  that  it  exhibits  far  greater  complexity  and  is  a  much 
more  highly  differentiated  structure.  Spermatozoa  also  difier  from 
cilia  in  being  highly  resistant  to  putrefaction  and  to  chemical  reagents, 
even  including  the  strongest  acids  and  alkalies. 

Spermogenesis. — The  spermatozoa  are  developed  from  the  small 
cells  (spermatids)  which  form  the  innermost  stratum  of  the  seminal 
epithelium,  and  these  are  themselves  produced  by  the  division  of 
the  large  spermocytes  of  the  second  layer.  It  is  probable  that  fresh 
spermocytes  are  formed  by  division  of  some  of  the  lining  epithelium- 
cells  or  spermogons.  The  cycle  of  changes  therefore  which  takes  place 
is  as  follows: — 1.  Division  of  a  lining  epithelium-cell  or  spermogon 
into  two,  one  of  which  grow\s  larger  ("growing  cells  "  of  H.  H.  Brown), 
becomes  a  spermocyte,  and  passes  into  the  second  layer,  while  the 
other  remains  in  the  first  layer.  2.  Division  of  the  spermocyte. 
3.  Further  division  of  the  daughter-spermocytes  thus  produced.  The 
four  cells  (spermatids)  which  result  from  this  double  division  possess  only 
one-half  the  somatic  number  of  chromosomes  in  their  nuclei,  "reduc- 
tion" having  been  effected  in  the  final  cell-divisions  by  which  the 
spermatids  are  produced  (see  p.  14).  4.  Elongation  of  the  spermatids 
and  their  gradual  conversion  into  spermatozoa.  As  they  undergo  this 
conversion  their  grouping  becomes  more  evident,  and  each  group  is 
found  to  be  connected  with  a  cell  of  Sertoli  (figs.  414,  a,  417), 
which  probably  ministers  to  their  nutrition.  This  cell  undergoes  a 
gradual  process  of  elongation  so  that  the  spermatozoa  by  the  time 
they  are  fully  developed  are  brought  to  the  lumen  of  the  tube, 
in  which  they  then  become  free.  In  the  meantime  other  alternate 
groups  of  spermatids  from  which  the  next  crop  of  spermatozoa  will 
be  derived  are  being  formed  in  the  same  manner,  passing  through 
the  same  cycle  of  changes.  So  that  in  a  longitudinal  section  even 
of  the  same  tubule,  different  phases  of  development  may  be  observed, 
and  in  different  tubules  of  the  same  testicle  every  phase  may  be 
traced.  The  accompanying  diagram  (fig.  414),  which  is  constructed 
from  drawings  by  H.  H.  Brown,  illustrates  the  cj^cle  of  changes 
above,  described :  it  is  divided  into  eight  parts,  each  of  which  shows 


342 


THE   ESSENTIALS   OF  HISTOLOGY. 


the    condition    of    the    epithelium    of   a    seminiferous    tubule    at    a 
particular  stage. 

Each  spermatid  becomes  converted  into  a  spermatozoon  in  the 
following  manner  (figs.  415,  416,  418).  The  nucleus  forms  the 
chief  part  of  the  head,  while  the  tail  develops  as  an  outgrowth  of 
the  centrosome  and  cytoplasm.  The  tail-filament  appears  within  the 
protoplasm,  growing  out  from  the  centriole  of  the  cell  which  lies  close 


Fig.  418. 
Fig.  417. — A  cell  of  Sertoli  with  which  the  spermatids  (three  of  which 

ARE  shown)  ARE  BEGINNING  TO  BE  CONNECTED  :    HUMAN.      (Bramman.) 
The  cell  contains  globules  (of  nutritive  substance)  staining  with  osmic  acid,  and  similar 
but  smaller  globules  are  also  seen  in  the  spermatids.     The  "  ring"  formed  around  the 
tail  filament  by  one  of  the  particles  uf  the  centrosome  (see  text)  is  shown  in  each  of 
these  spermatids  close  to  the  "  head.'' 

Fig.  418.— Stages  of  spermogenesis,  with  transformation  of  the  granules 
OR  mitochondria  of  the  spermatid  into  the  spiral  fibre  of  the  middle 
PIECE:  MOUSE.      (Benda.) 

to  the  nucleus  (fig.  416).  The  centriole  is  double,  and  one  of  its  two 
particles  forms  an  annular  expansion  or  ring  which,  as  development 
proceeds,  moves  down  the  tail-filament  until  it  reaches  the  place  where 
this  leaves  the  cytoplasm  :  here  it  ultimately  forms  the  limit  of  the 
body  or  middle  piece  of  the  spermatozoon.  The  archoplasm  (see  p.  8) 
assists  in  forming  the  head  of  the  spermatozoon ;  a  portion  (the 
idiozome  of  Moves)  at  an  early  stage  separates  from  the  rest,  lying 
apically  to  the  nucleus.  Within  this  portion  vacuoles  form  (fig. 
416,  b,  c,  d)  which  presently  run  together  into  a  clear  non-stainable 


SPERMOGENESIS.  343 

glol)ule  wliieh  tluttons  out  over  the  nucleus  and  forms  (fig.  416,  e)  the 
head-cap  of  the  spermatozoon ;  as  development  proceeds,  this  may 
become  indistinguishable  from  the  rest  of  the  head.  The  spiral  fibre 
of  the  middle  piece  is  developed  from  mitochondria  (see  p.  5)  in  the 
spermatid  (Benda)  (fig.  418). 

A  portion  of  the  protoplasm  of  each  spermatid  containing  a  number 
of  chromatin-particles  (seminal  granules)  becomes  detached  and  disin- 
tegrated before  the  spermatozoon  is  fully  matured  (fig.  414,  s,  .s'). 

A  few  spermocytes  undergo  incomplete  division,  and  the  resulting 
spermatids  are  large  (giant  spermatids)  and  contain  either  one  large 
nucleus  or  two  or  more  nuclei  which  ultimately  blend  to  form  the 
head  of  the  spermatozoon.  In  these  cases  there  are  a  corresponding 
number  of  centrosomes,  from  each  of  which  a  tail-filament  may  become 
developed. 


344  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    XXXVIII. 

GENERATIVE  ORGANS   OF  THE  FEMALE. 

1.  Sections  of  the  ovary  of  the  non-pregiiaut  rabbit  or  cat.  (If  from  a 
pi-egnant  animal  the  organ  may  be  largely  occupied  by  luteal  tissue.) 
Study  the  sections  with  a  low  power,  observing  the  small  and  large 
Graafian  follicles,  each  inclosing  an  ovum,  scattered  through  the  stroma. 
Measure  some  Graafian  follicles  of  different  sizes  ;  make  a  general  sketch 
of  a  section  under  the  low  power.  Then  sketch  carefully  two  or  more  of 
the  follicles  with  their  contents  under  a  high  power. 

2.  Sections  across  the  Fallopian  tube.  Sketch  a  section  under  the  low 
power. 

3.  Section  across  the  body  of  the  uterus,  or  across  a  cornu  of  a  bicorued 
uterus.  Observe  with  the  naked  eye  the  thickness  of  the  muscular  and 
mucous  coats  respectively.  Notice  the  ciliated  columnar  epithelium  lining 
the  organ  and  extending  into  the  glands  of  the  mucous  membrane.  Draw 
a  part  of  the  section  under  the  low  power. 

4.  Section  of  the  mucous  membrane  of  the  vagina.  Notice  the  stratified 
scaly  epithelium  which  lines  it  and  which  is  continued  over  the  projecting 
part  of  the  os  uteri. 

5.  Take  the  fresh  ovary  of  a  recently  killed  animal  aud  with  a  needle  or 
fine  scalpel-point  prick  one  of  the  largest  and  most  prominent  of  the  Graafian 
follicles.  The  organ  must  be  held  just  over  a  slide  so  that  on  pricking  the 
follicle  the  fluid  contents  may  spui't  out  on  to  the  glass.  E.xamine  tlie  drop 
of  liquor  folliculi  with  a  low  power  for  the  escaped  ovum,  which  will  be 
surrounded  by  follicular  cells.  When  found  place  a  piece  of  hair  in  the 
drop,  cover  with  cover-glass  and  examine  with  high  ])ower. 


THE   OVARY. 

The  ovary  is  a  small  solid  organ,  composed  of  a  stroma  of  fibrous 
tissue,  with  many  spindle-shaped  cells,  and  also  containing,  near  its 
attachment  to  the  broad  ligament,  a  large  number  of  plain  muscular 
fibres.  It  is  covered  by  a  layer  of  small  columnar  epithelium-cells 
{germinal  epithelium,  fig.  420,  a),  between  which  may  here  and  there 
be  seen  a  few  larger  spheroidal  cells,  with  large  round  nuclei.  In 
the  young  subject  the  epithelium  occasionally  dips  down  into  the 
subjacent  stroma. 

The  stroma  is  beset  wath  vesicles  of  diflferent  sizes,  the  smallest 
being  near  the  surface  of  the  organ,  the  larger  ones  placed  more 
deeply  in  the  stroma,  although,  as  they  increase  in  size,  they  extend 
towards  the  surface. 


THE   OVARY. 


346 


These  vesicles  ave  tlie  Graafian  foJlides.  Each  Gruafiaii  follicle  has 
a  proper  wall  (theca  follicuU)  formed  of  a  layer  derived  from  the  stroma, 
and  a  special  inner  layer  containing  large  cells :  both  are  highly 
vascnlar.  Each  follicle  contains  an  ovum  and  epitheliiun.  In  the 
smallest  follicles  the  ovum  is  small,  and  the  epithelium  of  the  follicle 
is  formed  of  a  single  layer  of  cells,  which  may  be  flattened  against 
the  ovum  (fig.  421).  In  somewhat  larger  follicles  the  epithelium-cells 
are  in  two  layers,  and  these  are  columnar  in  shape  (fig.  423,  E).  In 
still  larger  ones,  each  of  these  two  layers  is  formed  of  several  strata  of 
cells,  and  fluid  has  begun  t-o  collect  between  the  layers  at  one  part.  Of 
the  two  layers,  the  one  which  lines  the  cavity  of  the  follicle  is  termed 
the  memhrana  granulosa,  while  the  mass  of  cells  which  more  immediately 
surrounds  the  ovum  is  known  as  the  cumulus  or  discus  proligerus. 


Fig.  419. — Section  of  the  ovary  of  the  cat.     J.    (Schron.) 

1,  outer  covering  and  free  border  of  the  ovary  ;  1' ,  attached  border  ;  2,  tlie  central  ovariau 
stroma,  showing  a  fibrous  and  vascular  structure ;  3,  peripheral  sti-oma  ;  U,  blood- 
vessels ;  5,  Graafian  follicles  in  their  earliest  stages  Ij'ing  near  the  surface  ;  6,  7,  S, 
more  advanced  follicles  which  are  embedded  more  deeply  in  the  stroma  ;  9,  an  almost 
mature  follicle  containing  the  ovum  in  its  deepest  part  ;  9' ,  a  follicle  from  which  the 
ovum  has  fallen  out  in  preparing  the  section  ;  10,  coi-pus  luteum. 


In  the  largest  follicles  the  fluid  has  much  increased  in  amount,  so 
that  the  follicle  has  become  gradually  larger  and  more  tense.  Finally 
it  reaches  the  surface  of  the  ovary,  and  projects  from  that  surface, 
where  it  eventually  bursts,  and  the  liquor  folliculi,  with  its  contained 
ovum,  is  set  free.  This  event  is  believed  to  occur  usually  at  some  time 
during  menstruation. 

Some  of  the  Graafian  follicles  do  not  burst,  but,  after  attaining  a 
certain  stage  of  maturity,  undergo  a  process  of  retrograde  metamor- 
phosis and  eventually  disappear. 

The  ovarian  ova  or  ovocytes  are  large  spherical  cells  (fig.  424), 
about  0  2  mm.  {^\-g  inch)  in  diameter.     When  fully  formed,  as  in  the 


346 


THE   ESSENTIALS   OF   HISTOLOGY. 


largest  Graafian  follicles,  each  ovum  is  surrounded  by  a  thick  trans- 
parent membrane  {zona  pellucida).  Within  this  is  the  protoplasm  of 
the  ovocyte  (vitellus),  filled  with  fatty  and  albuminous  granules  (yolk 
granules).     Lying  in  the  vitellus,  generally  eccentrically,  is  the  large 


Fig.  420.— Section  of  the  ovary  of  an  adult  bitch.     (Waldever.) 

a,  germ-epithelium  ;  h,  remains  of  egg-tubes ;  c,  small  follicles  ;  d,  more  advanced  follicle  ; 
e,  discus  proligerus  and  ovum  ;  ./;  second  ovum  in  the  same  follicle  (this  occurs  but 
rarely);  g,  outer  tunic  of  the  follicle;  h,  inner  tunic;  i,  membrana  granulosa;  k, 
collapsed  retrograded  follicle;  I,  blood-vessels;  in,  m,  longitudinal  and  transverse 
sections  of  tubes  of  the  parovarium  ;  y,  involuted  portion  of  the  germ-epithelium  of 
the  surface ;  z,  place  of  the  transition  from  peritoneal  to  germinal  or  ovarian 
epithelium. 

clear  round  nucleus  {germinal  vesicle),  which  may  show  an  intranuclear 
network,  and  invariably  has  a  well-marked  nucleolus  {germinal  spot), 
sometimes  more  than  one. 

Oogenesis. — Both  the  ova  and  the  epithelium  of  the  Graafian  follicles 


THE   OVARY. 


347 


originate  from  the  germinal  epithelium  of  the  embryo.  This  forms  at 
first  a  simple  layer  covering  the  stroma,  but  later  becomes  thickened 
and  multiple.  After  a  time  rounded  cords  of  epithelium-cells  {pjjfj- 
tiibes  of  Pfliiger  ;  fig.  423,  A),  i^row  down  into  the  stroma,  whilst  this 


TJ-  '.jv  ij-r\r'i:i^/j  i  \<=' 


iyTT^HT'.rr/z/:. ,_  w.< 


yM^^^- 


Fig.  421. — Section  of  part  of  human  ovary  sHowiNd  small  Graafian 

FOLLICLES    IMBEDDED    IN    A    FIBRO-CELLCLAR   STROMA.       (Sellheim.) 


Fig.  422.— a  moderately  large  Graafian  follicle  from  the  human  ovary, 
showing  ovum  surrounded  by  '"discus  proligerus  "  and  wall  of  follicle 

LINED   BY    "MEMBRANA  GRANULOSA."      BETWEEN   THEM   IS   AN   ACCUMULATION 

OF  LIQUOR  FOLLICULI.     (Sellheim.) 


348 


THE   ESSENTIALS   OF   HISTOLOGY. 


at  the  same  time  grows  into  the  epithelium.      The  cords  presently 
become  broken  up  by  ingrowths  of  stroma  into  small  isolated  nests  of 


Fig.  423. — Figures  showing  various  stages  in  the  developjient  of  the 
Graafian  follicles  of  the  rabbit. 

A,  from  ovary  of  young  rabbit,  showing  "  egg-tubes  "  of  Pfiiiger  gi-owing  iu  from  germinal 
epithelium  ;  some  of  the  tubes  contain  primitive  ova ;  b,  pi-imitive  Graafian  follicles 
formed  from  the  breaking  up  of  an  egg-tube  ;  c,  a  young  Graafian  follicle,  with  a 
single  layer  of  follicle-epithelium  ;  D,  a  somewhat  older  follicle,  with  the  second  layer 
forming  within  the  first ;  e,  a  more  advanced  follicle,  showing  two  complete  layers  of 
columnar  epithelium  surrounding  the  ovum  within  the  follicle. 


epithelium-cells,  each  of  which  may  represent  a  Graafian  follicle.  To 
form  the  ova,  some  of  the  cells  become  enlarged  (primitive  ova), 
and  usually  there  is  one  such  enlarged  cell  in  each  of  the  isolated 


THE   OVARY. 


349 


nests.^  The  remaining  cells  form  the-  epithelium  of  the  follicle  (see 
fig.  42'S,  B,  g).  It  is  stated  that  the  protoplasm  of  the  ovum  remains 
connected   with   the  cells  of  the  discus  proligerus  by    fine  processes 


0\^\\\  'r 


Fig.  424.— Human  ovum;  highly  magnified.     (Wakleyer.) 
The  zona  pellucida  is  surrounded  by  cells  of  the  discus  proligerus,  which  are  adherent  to  it. 


which  pass  through  pores  in  the  zona  pellucida,  and  on  the  other 
hand,  the  epithelium-cells  of  the  follicle  are  themselves  inter-connected 
by  protoplasmic  bridges,  so  that  the  whole  forms  a  syncytium. 

1  The  nuclei  of  the  primitive  ova  pass  through  the  pre-inaiotic  changes  mentioned 
on  p.  14. 


350 


THE   ESSENTIALS   OF   HISTOLOGY 


The  stroma  of  the  ovary  contains,  besides  the  spindle-shaped  con- 
nective-tissue cells  and  plain  muscular  fibres  already  mentioned,  a 
number  of  epithelium-like  interstitial  cells.  Some  of  these  are  derived 
from  the  germinal  epithelium,  and  appear  capable  of  developing 
into  ova  and  follicle  epithelium-cells  (Lane-Claypon) ;  others  have 
originated  from  cells  of  corpora  lutea.      These  last  are  large  yellow 


Fig.  425. — Three  stages  ix  the  for- 
mation' OF  THE  CORPUS  LCTEUM  IN 
THE   MOUSE.       (Sobotta.) 

A.  The  follicular  epithelium,  fe,  is  hyper- 
trophied,  and  vascular  processes,  a,  of  the 
theca,  th,  or  wall  of  the  follicle  are  growing 
into  it. 

The  epithelial  mass  is  now  subdivided 
into  loVjule-like  masses,  /,  of  luteal  cells  by 
the  thecal  ingrowths ;  e,  epithelium  of 
surface  of  ovary. 
C.'  There  are  now  very  numerous  thecal 
septrt.  or  trabeculaj,  and  the  columns  of 
luteal  cells  are  much  narrower.  A  central 
cavity  is  still  seen. 


nodules  which  are  developed  out  of  the  Graafian  follicles  after  the 
ova  have  been  extruded  (figs.  425,  426).  They  consist  of  columns  of 
large  yellowish  cells  {luteal  cells),  with  intervening  trabecul^e  of  vascular 
fibrous  tissue,  which  converge  to  a  central  strand  of  connective  tissue 
occupying  the  axis  of  the  nodule  (fig.  426).  The  columns  of  cells 
are  not  unlike  those  of  the  cortex  of  the  suprarenal  capsule.  The 
corpus  luteum  is  derived  from  the  wall — probably  in  the  main  from 
the  epithelium — of  the  follicle,  which  becomes  thickened  and  folded 
by  multiplication  and  hypertrophy  of  its   cells  ;    between  the   folds 


THE   OVARY. 


351 


connective  tissue  and  blood-vessels  grow  in  from  the  theca  towards 
the  centre  of  the  follicle  ;  in  this  way  the  columnar  arrangement 
above  mentioned  is  produced.  After  persisting  for  a  time  the  corpus 
luteum  gradually  disappears,  its  tissue  becoming  merged  in  the 
surrounding  stroma.  Corpora  lutea  grow  much  larger  and  remain 
much  longer  persistent  in  the  event  of  pregnancy  supervening. 


\ 


Fig.  426. — Corpus  lcteum  of  jiocse.     (Sobotta.) 

This  figure  shows  a  more  advanced  stage  of  development,  the  luteal  tissue  being  now 

vascularized  and  the  central  cavity  obliterated. 

The  use  of  the  corpus  luteum  is  not  known  certainly,  but  it  has  recently 
been  suggested  that  it  may  yield  an  internal  secretion,  the  effect  of  which 
is  to  produce  the  fixation  of  the  fertilized  ovum  in  the  uterine  mucous 
membrane  (Born).  In  confirmation  of  this,  experiments  seem  to  indicate 
that  gestation  does  not  supervene  in  animals  whose  corpora  lutea  have  been 
destroyed  (Fraenkel  and  Cohn),  or  from  which  the  ovaries  have  been  removed 
during  the  first  stages  of  pregnancy  (Marshall  and  Jolly). 

The  blood-vessels  of  the  ovary  are  very  large  and  numerous,  and  are 
especially  distributed  to  the  walls  of  the  Graafian  follicles,  over  -which  they 
form  a  close  network. 


THE  FALLOPIAN  TTBES  AND  UTERUS. 

The  Fallopian  tubes  are  lined  by  a  very  vascular  mucous  membrane 
which  is  covered  with  ciliated  epithelium,  and  has  numerous  longi- 
tudinal folds  (fig.  427).  Externally  they  are  covered  by  a  serous 
coat,  within  which  is  a  thin  longitudinal  stratum  of  plain  muscular 


352 


THE   ESSENTIALS  OF  HISTOLOGY. 


fibres  overlying  circular  fibres  of  the  same  tissue,  but  these  layers  are 
not  distinctlj'  marked  off"  from  one  another. 

The  human  uterus  is  composed  of  two  parts,  the  body  and  cervix. 
The  body  of  the  uterus  is  formed  of  the  following  layers  : 

L  A  seroua  layer,  derived  from  the  peritoneum,  which  covers  the 
greater  part  of  the  fundus. 

2.  A  muscular  laiier,  which  is  of  considerable  thickness  and  is  formed 
of  plain  muscular  fibres  disposed  in  three,  more  or  less  blended,  strata. 
Of  these  the  outer  has  its  fibres  arranged  partly  longitudinally,  partly 
circularly.     The  middle  muscular  layer,  on  the  other  hand,  is  thick  ; 


Fio.  427.— Section  across  the  fallopian  tcbe.     (Diagrammatic.) 

its  fibres  run  in  different  directions,  and  it  contains  the  ramifications 
of  the  larger  blood-vessels.  The  inner  layer,  again,  is  thinner  and  has 
both  longitudinal  and  circular  fibres,  many  of  the  latter  being  pro- 
longed internally  into  the  deeper  part  of  the  mucous  membrane ;  the 
extremities  of  the  uterine  glands  extend  between  and  amongst  its 
fibres. 

3.  A  mucous  membrane,  which  is  ver}'  thick  and  is  composed  of  soft 
connective  tissue  containing  a  large  number  of  spindle-shaped  cells.  It 
is  lined  by  ciliated  epithelium  and  contains  long,  simple,  tubular 
glands,  which  take  a  curved  or  convoluted  course  in  passing  through 
the  membrane  (fig.  429).  Their  (ciliated)  epithelium  is  continuous  with 
that  which  covers  the  inner  surface  of  the  mucous  membrane.  In  the 
cervix  the  mucous  membrane  is  marked  by  longitudinal  and  oblique 
ridges,  and  the  glands  are  shorter  but  more  complex  than  those  of  the 


THE   FALLOPIAN  TUBES. 


353 


Fi( 


Sii 


!•)> 


MX'TION  OF  MUCOUS  MEMBRANE  OF  HUMAN  UTERUS  DURING  MEN- 
STRUATION, SHOWING  MASSES  OF  BLOOD  WHICH  HAVE  ESCAPED  PROM  RUPTURED 
CAPILLARIES  INTO  THE  INTEKGLANDULAR  TISSUE,  AND  HAVE  AT  ONE  PLACE  (*) 
BROKEN    THROUGH    THE   SURFACE   EPITHELIUM.       (Sellheim.) 


Fig.  429. — Section  of  a  cornu  of  the  babbit's  uterus. 

serous  layer;  l.ni.,  longitudinal  muscular  fibres;  cm.,  circular  muscular  fibres  of  the 
muscular  coat ;  (i,  areolar  tissue  with  large  blood-vessels;  m.m.,  muscularis  mucosie  ; 
iH,  mucous  membrane. 

Z 


354 


THE   ESSENTIALS  OF   HISTOLOGY. 


body  of  the  uterus,  and  are  lined  by  columnar  mucus-secretin 
cells.  Near  the  os  uteri  the  epithelium 
becomes  non-ciliated  columnar,  and  at  the 
margin  of  the  os  uteri  this  passes  into  a 
stratified  epithelium  which  overlies  vascular 
papillae  of  the  cerium.  The  mucous  mem- 
brane is  very  vascular,  and  it  also  contains  a 
large  number  of  lymph -vessels. 

In  many  animals  the  uterus  is  composed  of 
two  long  tubes  (cornua  uteri) :  the  arrange- 
ment of  the  muscular  tissue  in  these  is  simpler 
than  in  the  human  uterus,  which  has  been 
formed  by  the  fusion  of  two  such  tubes. 
Fig.  429  exhibits  the  structure  of  a  cornu  of 
the  uterus  of  the  rabbit. 

At  each  menstrual  period  the  mucous 
membrane  of  the  uterus  undergoes  a  partial 
process  of  disintegration  accompanied  by  an 
escape  of  blood  from  the  capillaries  of  the 
membrane  (fig.  428).  This  is  succeeded  by 
a  rapid  renewal  of  the  disintegrated  part. 
Should  gestation  supervene,  the  process  of 
renewal  results  in  the  formation  over  certain 
parts  of  a  greatly  thickened  mucous  mem- 
brane, with  long  convoluted  glands,  which  is 
then  known  as  the  decidua.  The  muscular 
layer  also  becomes  enormously  hypertrophied, 
this  hypertrophy  being  produced  by  the 
Fig.    430.  —  Muscular     enlargement    of    the    individual    muscle   cells 

FIBRES   (a)   FROM   NON-  .  a\ 

PREGNANT,  (6)  FROM  PREG-    (fig.  430). 
NANT  UTERUS,  DRAWN  TO 
THE  SAME  SCALE.   (Sell- 

heim. ) 


THE   SPINAL  CORD.  355 


LESSONS   XXXIX.   AND    XL. 

STRUCTURE  OF   THE  SPINAL    CORD. 

].  Sectioxs  of  the  spinal  cord  from  the  cervical,  dorsal,  and  lumbar  regions. 
If  the  human  spinal  cord  cannot  be  obtained  sufficiently  fresh,  that  of  a 
dog,  cat,  or  monkey  may  be  used.  It  is  to  be  hardened  by  suspending  it 
immediately  after  removal  from  the  body  in  a  tall  jar  of  formol  (10  per  cent, 
solution).  After  a  few  days  it  may  be  transferred  to  alcohol.  Sections  are 
to  be  made  either  by  the  paraffin  or  celloidin  method  :  the  former  is  prefer- 
able for  small  cords.  The  sections  may  be  stained  by  Nissl's  method,  which 
brings  to  view  the  nerve-cells  and  also  stains  the  axis-cylinders  of  the  nerve- 
fibres.  If  it  is  desired  to  stain  by  the  Weigert-Pal  method,  which  colours 
the  medullary  sheaths  of  the  nerve-fibres,  the  pieces  of  cord  should  be  placed 
in  2  per  cent,  bichromate  of  potassium  solution  or  Miiller's  fluid  (either  at 
once  or  after  formol)  and  should  be  left  for  about  a  month,  after  which  they 
are  cut  by  a  freezing  microtome.  (For  the  details  of  these  methods  see 
Appendix.)  Carminate  of  ammonia  or  thionin  may  also  be  employed  to 
stain  the  nerve-cells  and  axis-cylinders. 

Notice  the  relative  extent  of  the  grey  as  compared  with  the  white  matter 
in  the  different  regions  of  the  cord. 

Sketch  a  section  from  each  region  under  a  low  power.  Sketch  also  a 
small  portion  of  the  white  substance,  two  or  three  nerve-cells,  and  the  central 
canal  with  its  lining  epithelium  and  surrounding  neuroglia  under  the  high 
power. 

Measure  the  diameter  of  some  of  the  nerve-fibres  in  the  anterior  columns, 
in  the  lateral  columns,  and  in  the  posterior  columns. 

2.  Tracts  in  the  spinal  cord.  The  conducting  tracts  of  the  spinal  cord  may 
be  studied  in  two  ways,  viz.  :  (1)  by  preparing  sections  of  embryonic  cords 
(from  the  5th  to  the  9th  mouth),  the  sections  being  stained  by  the  Weigert-Pal 
process  (Flechsig's  method)  ;  (2)  by  preparing  .sections  from  the  cord  of  an 
animal  in  which  either  a  complete  section  or  a  hemi-section  has  been  performed 
about  15  days  before  the  animal  is  killed,  and  staining  thin  pieces  of  the 
cord  from  below  and  from  above  the  section  by  placing  them  in  a  solution 
consisting  of  two  parts  of  Miiller's  fluid  and  1  part  of  1  per  cent,  osmic  acid 
(Marchi's  method).  The  cord  must  first  be  partly  hardened  by  placing  it  for 
a  few  days  in  Miiller's  fluid. 


The  spinal  cord  is  composed  of  grey  matter  in  the  centre  and  of 
white  matter  externally.  It  is  closely  invested  by  a  layer  of  connective- 
tissue  containing  numerous  blood-vessels  {pia  mater),  and  less  closely 
by  two  other  membranes  (fig.  431).  One  of  these  is  an  areolar  mem- 
brane, resembling  a  serous  membrane  in  general  structure,  but  non- 
vascular and  more  delicate  in  texture  {arachnoid).  The  other,  which 
lines  the  vertebral  canal,  is  a  strong  fibrous  membrane  known  as  the 
dura  mater.     At  the  middle  of  the  anterior  and  posterior  (ventral  and 


356 


THE   ESSENTIALS   OF  HISTOLOGY. 


dorsal)  surfaces  the  pia  mater  dips  into  the  substance  of  the  cord  in  the 
anterior  and  j^osterior  median  fissure.^,  so  as  to  di\'ide  it  almost  completely 
into  two  lateral  halves.  These  are,  however,  united  by  an  isthmus  or 
bridge,  which  is  composed  anteriorly  of  transversely  crossing  white 
fibres  (white  or  anterior  amwmsure),  posteriorly  of  grey  matter  {grey 
commissure),  in  the  middle  of  which  is  a  minute  canal  lined  by  ciliated 
epithelium  (central  canal). 

Each  lateral  half  of  the  spinal  cord  contains  a  crescent  of  grey 
matter,  which  is  joined  to  the  corresponding  crescent  of  the  opposite 
side  by  the  grey  commissure.  Of  the  two  horns  of  the  crescent  the 
posterior  or  dorsal  is  the  narrower  and  comes  near  the  surface  of  the 


3^ 


Fig.  431.— Section  of  the 
spinal  cord  within  its 
IIEMBRANES.  (Key  and 
Retzius. ). 

II,  duva  luater  ;  b,  arachnoid ; 
'•,  .septum  of  arachuoid  ;  d,  e, 
tr.iliecula;  of  arachnoid ;  g, 
ligamciitum  denticulatum ; 
/,  bundles  of  posterior  root ; 
h,  bundles  of  anterior  root ; 
k,  I,  subarachnoid  space. 


cord  ;  close  to  it  the  bundles  of  the  posterior  nerve-roots  enter  the 
cord.  The  Ijundles  of  the  anterior  nerve-roots  emerge  from  the 
anterior  horn. 

According  to  Ingbert  about  1,300,000  nerve-fibres  enter  the  cord  by  the 
posterior  roots,  and  about  one-tliird  that  number  leave  it  by  the  anterior 
roots. 

The  posterior  root-fibres  are  derived  from  the  cells  of  the  spinal  ganglia, 
which  lie  out.side  the  cord;  the  anterior  root-fibres  from  cells  v^ithin  the 
grey  matter,  cliiefly  from  cells  in  the  anterior  horn,  but  also  from  some  cells 
in  tlie  middle  and  posterior  parts  of  the  grey  matter  and  (especially  in  tlie 
thoracic  region)  from  cells  in  the  intermedio-lateral  tract  (lateral  horn).  The 
latter  probably  furnish  the  autonomic  (sympathetic)  fibi'es  of  the  anterior 
roots,  while  the  cells  of  the  anterior  horn  furnish  the  fibres  which  are 
distributed  to  the  voluntary  muscles. 

The  v}iite  matter  of  each  half  of  the  cord  is  subdivided  by  the 
approach  of  the  posterior  horn  to  the  surface  into  two  unequal 
columns — antero-lateral  and  posterior.  A  distinction  is  sometimes 
drawn    between    anterior    and    lateral    portions    of  the    antero-lateral 


THE   SPINAL   CORD. 


357 


pustero-lateral  fissui 
postcro-inusial  column 

postero-niediau  fissur 

postcridi-  root-bundl 

posterior  colmiii 

subst.  gelat.  of 

post,  liurn  ^'■' 

tractof  Fluclisiu     J 

lat.  pyram.  tr    _j 

form.  retic._ 

lateral  liorii  _ 

central  canal  - 

aut.  commissun 

anterior  horn  — 

ant.  median  fissure 


Fig.  432. — Section  of  human  .spinal  cokd  from  upper  cervical  region. 
(Photograph.)     Magnified  about  8  diameters. 


f.a 


•         e  • 


s>^ 


.    ^,         . 


«      • 


Fig.  433.— a  small  portion  of  a  transverse  section  of  the  human  spinal 
coRu  in  the  region  of  the  lateral  column,  to  show  the  superficial 
neuroglia. 

a,  a,  s\iperficial  neuroglia  ;  b,  b,  transverse  section  of  part  of  the  lateral  column  of  the 
cord,  in  which  the  dark  points  are  the  axis-cylinders,  and  the  clear  areas  the 
medullary  substance  of  the  nerve-fibres.  The  superficial  neuroglia  is  seen  to  exhibit 
the  appearance  of  a  fine  feltwork  in  which  numerous  nuclei  and  one  or  two  corpora 
mw/iacea,  c.a.,  are  embedded,  and  to  extend  inwards  (c,  c)  among  the  nerve-fibres. 


358  THE   ESSENTIALS   OF   HISTOLOGY. 

column,  although  there  is  no  line  of  demarcation  between  them. 
In  the  upper  part  of  the  cord  the  posterior  column  is  subdivided 
by  a  septum  of  connective  tissue  into  two — the  poster o-mesial  column  or 
funiculus  gracilis,  and  the  postero-lateral  column  or  funiculus  cuneatus. 

The  white  matter  is  composed  of  longitudinally  coursing  medullated 
nerve-fibres,  which  in  sections  stained  with  carmine  or  thionin  appear 
as  clear  circular  areas  with  a  stained  dot,  the  axis-cylinder,  near  the 
middle  (fig.  433) ;  while  in  sections  stained  by  the  Weigert-Pal  method 
they  appear  as  black  circles  with  a  clear  centre.  The  nerve-fibres 
vary  in  size  in  different  parts ;  on  the  whole  those  which  are  nearest  to 
the  surface  of  the  cord  are  larger  than  those  nearest  to  the  grey 
matter,  but  there  is  a  bundle  of  very  small  fibres  (at  M,  fig.  434) 
opposite  the  tip  of  the  posterior  horn. 

The  medullated  fibres  are  supported  by  neuroglia,  which  is  com- 
posed of  fibrillated  neuroglia-cells  (fig.  192,  p.  161).  The  neuroglia  is 
accumulated  in  greater  amount  at  the  surface  of  the  cord,  underneath 
the  pia  mater  (particularly  in  the  human  cord,  near  the  entrance  of  the 
posterior  roots  (fig.  433)),  and  it  extends  into  the  grey  matter,  in  which 
it  is  especially  accumulated  in  the  substantia  gelatinosa  at  the  apex 
(caput)  of  the  posterior  horn  and  around  the  central  canal. 

The  grey  matter,  besides  neuroglia,  contains  an  interlacement  of 
nerve-fibres  and  the  arborisations  of  the  nerve-cells  which  are 
embedded  in  it. 

Characters  of  the  spinal  cord  in  the  several  regions  (figs.  434,  439). 
— In  the  cervical  region  the  white  matter,  especially  that  of  the  lateral 
columns,  occurs  in  largest  proportion.  The  grey  matter  in  the  cervical 
enlargement  is  also  in  considerable  amount,  and  it  encroaches,  especi- 
ally in  the  U[)per  part  of  the  region,  in  the  form  of  a  network  (foimatio 
reiimlaris)  upon  the  adjacent  part  of  the  lateral  white  column  (fig.  432). 
The  anterior  horns  are  thick  and  the  posterior  slender.  The  postero- 
mesial  column  is  distinctly  marked  off. 

In  the  dorsal  region  the  grey  matter  is  small  in  amount,  and  both 
horns  are  slender.  The  whole  cord  is  smaller  in  diameter  than  either 
in  the  cervical  or  lumbar  region.  The  columns  of  nerve-cells  known  as 
Clarke's  column  and  the  intermedio  lateral  tract  are  well  marked. 

In  the  lumba.r  region  the  crescents  of  grey  matter  are  very  thick, 
and  the  white,  substance,  especially  the  lateral  columns,  relatively 
small  in  amount.  The  isthmus  lies  nearly  in  the  centre  of  the 
cord,  whereas  in  the  cervical  and  dorsal  regions  it  is  nearer  the 
anterior  surface. 

In  the  part  of  the  spinal  cord  from  which  the  sacral  and  coccygeal 
nerve-roots   take   origin    the  grey   matter   largely   preponderates,   the 


THE   SPINAL   CORD. 


359 


/ 


Fig.  434. — Sections  of  human 
spinal  cord  from  the  lower 
cervical  (a),  mid-dorsal  (b), 
and  mid-lumbar  (c)  regions, 
showing  the  principal  groups 
of  nerve-cells,  and  on  the 
right  side  of  each  section 
the  conducting  tracts  as  thky 
occur  in  the  several  regions. 

6,  c,  groups  of  cells  of  the  anterior 
horn  ;  (7,  cells  of  the  lateral  horn  ; 
(',  middle  group  of  cells  ;  ,/,  cells  of 
Clarke's  column  ;  g,  cells  of  posterior 
horn ;  e,  c,  central  canal ;  a.c.  anterior 
commissure  ;  m,  marginal  bundle  of 
Lissauer  ;  p-ra,  septomarginal  tract. 


POSTERIOR 
ROOT 
BUNDLES 


360,  THE   ESSENTIALS   OF   HISTOLOGY. 

crescents  form  thick  irregular  masses,  and  the  grey  isthmus  is  also  of 
considerable  thickness. 

TRACTS    OF   NERVE-FIBRES    IN   THE   WHITE   COLUMNS. 

The  course  of  the  nerve-tracts  in  the  spinal  cord,  and  in  other  parts  of 
the  central  nervous  system,  can  be  made  out  by  the  method  of  Flechsig, 
which  involves  the  study  of  sections  of  the  developing  cord ;  for 
it  is  found  that  the  formation  of  medullary  substance  occurs  sooner 
in  some  tracts  than  in  others,  so  that  it  is  easy  to  make  out  the 
distinction  between  them.  Thus,  the  peripheral  nerves  and  nerve- 
roots  become  myelinated  in  the  first  half  of  the  fifth  month  of  foetal 
life.  Of  the  tracts  of  the  spinal  cord,  those  of  Burdach  and  Goll  (see 
below)  are  the  first  to  be  myelinated,  then  the  tracts  of  Flechsig  and 
Gowers,  all  of  these  being  sensory  or  centripetally  conducting,  while 
the  pyi-amidal  tracts,  which  are  motor  or  centrifugally  conducting, 
do  not  receive  their  myelin  sheath  until  after  birth.  ^ 

Another  method  (that  of  A.  Waller)  consists  of  investigating  the 
course  which  is  pursued  by  degeneration  of  the  nerve-fibres  in 
consequence  of  lesions  produced  accidentally  or  purposely.  Those 
tracts  in  which  degeneration  of  fibres  occurs  below  the  lesion  are 
termed  "descending"  tracts  ;  those  in  which  it  occurs  above  the  lesion 
are  termed  "ascending." 

The  cells  whence  the  fibres  of  any  tract  arise  can  be  identified  after  a 
lesion  of  the  tract  by  the  chromatolysis  or  degeneration  of  Nissl  which 
nerve-cells  undergo  after  section  of  their  axons  (see  pp.  154  to  L59). 

Tracts  of  the  posterior  column.  —  1.  Trad  of  Goll.  -  The  fibres  of  the 
poster o-mesial  colnmn  belong  to  a  tract  which  is  known  as  the  tract  of 
Goll  (fig.  435,  6).  This  consists  of  fibres  derived  from  the  posterior 
nerve-roots  of  the  sacral,  lumbar,  and  lower  dorsal  nerves,  which, 
after  having  entered  the  posterolateral  columns,  pass,  as  they  ascend, 
towards  the  posterior  median  fissure  aud  form  a  distinct  tract,  which  is 
marked  off  from  the  rest  of  the  posterior  column  in  the  cervical  region 
by  a  slight  furrow  and  a  septum  of  pia  mater  (fig.  432).  This  tract 
ends  amongst  the  cells  of  the  nucleus  gracilis  of  the  medulla  oblongata. 

2.  Tract  of  Burdach. — The  paste ro-lateral  column  (tract  of  Burdach)  is 
also  composed  of  fibres  of  the  posterior  nerve-roots,  which  all  run  for 
a  certain  distance  in  it  before  entering  the  grey  matter  of  the  cord 
or  of  the  medulla  oblongata.     As  each  mass  of  posterior  root-bundles 

^  Flechsig  finds  that  the  fibres  of  the  posterior  roots  are  myelinated  in  at  least 
three  stages,  and  that  the  postero-lateral  tract  shows  a  corresponding  differentia- 
tion into  three  chief  parts:  the  xx'ntral,  middle  and  dorsal  root-zones.  He  suggests 
that  this  differentiation  corresponds  with  functional  differences  of  the  fibres. 


THE   SPINAL   CORD. 


361 


s^L 


enters  the  column  close  to  the  apex  of  the  posterior  horn  it,  so  to 
speak,  pushes  the  root-fibres  which  have  already  entered  nearer  to 
the  median  fissure  ;  hence  those  which  are  derived  from  the  lowest 
nerve-roots  are  nearest  that  fissure  (in  the  tract  of  (tIoII),  while  those 
which  are  derived  from  the  highest  remain  near  the  posterior  horn 
(in  the  tract  of  Burdach).  Many  of  the  fibres  of  both  tracts  pass 
into  the  grey  matter  either  immediately  on  entering  the  cord  or 
in  their  course  upwards ;  the  rest  are  continued  into  the  medulla 
oblongata  and  those  of  the  tract  of  Burdach  end  by  arborising  amongst 
the  cells  of  the  nucleus  cunenhis. 

3.  Comma  trad. — Besides  the  tracts  of  Burdach  and  Goll,  which  are 
wholly  composed  of  long  "  ascending  "  fibres  having  their  cells  of  origin 

Fio.  435.— Diagram  showing 

THE  A.SCENniNG  (RIGHT  SIDE) 
AND  DESCENDING  (LEFT  SIDE) 
TRACTS  IN  THE  SPINAL  CORD. 
1 ,  Crossed  pyramidal ;  2,  direct 
pyramidal ;  3,  antero-lateral  de- 
scending ;  3a,  bundle  of  Helweg  ; 
4,  prepyramidal ;  5,  comma  ;  6, 
postero-mesial;  7,  postero-lateral; 
8,  tract  of  Lissauer  ; !',  dorsal  cere- 
bellar ;  10,  antero-latei-al  ascend- 
ing or  ventral  cerebellar ;  s-m, 
septo-inarginal  ;s.;)./.,superficiai 
postero-lateral  fibres  (dorsal  root 
zone  of  Flechsig) ;  a  to  i>5,  groups 
of  cells  in  the  anterior  horn  ;  (, 
intermedio-lateral  group  or  cell- 
column  in  the  lateral  part  of  the 
grey  matter  ;  p,  cells  of  posterior 
horn  ;  rf,  dorsal  nucleusof  Stilling 
or  cell-column  of  Clarke.  The 
fine  dots  indicate  the  situation  of 
"endogenous"  fibres  (arising  in 
grej'  matter  of  cord)  having  for 
the  most  part  a  short  course. 

in  the  ganglia  on  the  posterior  roots,  there  are  a  few  fibres  which  have 
a  shorter  "descending"  course  in  the  posterior  column.  These  are 
believed  by  some  authorities  to  arise  from  descending  branches  of  the 
posterior  root-fibres,  by  others  to  arise  from  cells  in  the  grey  matter 
of  the  cord.     They  form  the  so-called  com  ma  tract  (fig.  435,  5). 

Proprio-spinal  or  endogenous  fibres  of  the  posterior  column. — 
There  are  a  few  fibres  (septo-marginal),  chiefly  accumulated  near  the 
median  fissure  (oval  bundle)  and  near  the  posterior  surface  (median 
triangle  bundle),  but  also  scattered  in  other  parts  of  the  column, 
which  are  derived  from  cells  in  the  grey  matter  of  the  cord  itself. 
These  take  a  "descending"  course  in  the  postei-ior  column;  while 
others  which  arise  in  the  grey  matter  and  have  an  "  ascending " 
course  arc  especially  numerous  in  the  ventral  part  of  the  column. 

Descending  tracts  of  the  antero-lateral  column. — 1.  Pyramidal  or 
corticos/iinal  tract. — At  the  posterior  part  of  the  lateral  column  there 
is  a  tract  of  moderately  large  "descending"  fibres  (intermingled  with 


362 


THE   ESSENTIALS   OF  HISTOLOGY. 


CEREBELLAR 
HEMISPHERE 


Fig.  436.— Diagram  showing  the  course,  origin,  and  termination  of  the 

fibres  of  the  principal  tracts  of  the  white  matter  of  the  spinal 

CORD.     (The  numliers  in  this  diHgram  refer  to  fibies  of  the  tracts  showa 

with  correspondiiig  numbers  in  fig.  435.) 

"  Descending"  tracts  :—  In,  a  fibre  of  the  crossed  pj-ramidal  tract ;  lb,  an  uncrossed  fibre  of 

the  pyramidal  tract  passing  to  the  lateral  column  of  the  same  side  ;  S,  a  fibre  of  the 

dii-ect  pyramidal  tract;  5,  a  fibre  of  the  anterolateral  descen'iing  tract ;  i,  a  fibre  of 

the  prepyramidal  tract;    5,  fibres  of  the  comma  tract.     "Ascending"  tracts:— 6.  a 

fibre  of  the  postero-mesial  tract ;  7,  fibres  of  the  postero  lateral  tract ;  9,  one  belonging 

to  the  dorsal  cerebellar ;  10,  a  fibre  of  the  ascending  antero-lateral  or  ventral  cerebellar 

tract.     Also,  )k,  motor  nerves  ;  s,  sensory  (afferent)  nerves. 


THR   SPINAL  CORD.  363 

smaller  fibres)  which  are  found  to  run  in  the  lateral  column  of  the 
spinal  cord  from  the  opposite  side  of  the  brain,  after  having  for  the 
most  part  crossed  at  the  decussation  of  the  pyramids  of  the  medulla 
oblongata  (cro.tsed  lateral  pyramidal  trad,  fig.  435,  1 ;  fig.  436,  la)- 
Intermingled  with  the  fibres  of  the  crossed  pyramidal  tract  in  the 
lateral  column  are  a  few  fil)res  of  the  pyramid  which  have  not  crossed 
in  the  medulla  oblongata,  and  which  are  therefore  derived  from  the 
cerebral  cortex  of  the  same  side  (uncrossed  lateral  pyramidal  fibres, 
fig.  436,  lb).  The  large  fibres  which  lie  in  the  anterior  columns  next 
to  the  anterior  median  fissure,  which  are  especially  numerous  in  the 
upper  part  of  the  human  coid,  also  l)elong  to  a  portion  of  the  same 
tract  which  has  not  undergone  decussation  {direct  pyramidal  tract, 
figs.  435,  436,  2).  The  direct  pyramidal  tract  is  only  found  in  man 
and  the  anthropoid  apes ;  in  some  individuals  it  is  absent,  and  it 
varies  considerably  in  extent. 

The  pyramidal  tracts  are  composed  of  "  descending "  fibres,  which 
have  their  cells  of  origin  in  the  cerebral  cortex  (ascending  frontal 
and  paracentral  gyri)  and  end  by  arborisations  in  the  grey  matter 
at  the  base  of  the  postei'ior  cornua  of  the  spinal  cord.  In  some 
mammals  (rat,  mouse,  guinea  pig,  sheep,  kangaroo,  squirrel,  etc.),  the 
pyramidal  tracts  are  situated  in  the  posterior  columns  of  the  cord, 
in  others,  including  the  monkey,  dog,  cat,  and  rabbit,  they  run  in  the 
lateral  columns  The  pyramidal  tracts  are  very  small  in  the  lower 
mammals,  and  are  not  found  at  all  in  vertebrates  below  mammals. 

It  has  been  calculated  that  there  are  about  80,000  fibres  of  the 
pyramidal  tract  in  each  half  of  the  human  cord.  The  pyramidal  tracts 
are  generally  regarded  as  the  paths  along  which  volitional  impulses  are 
conveyed  from  the  cerebral  cortex  to  the  spinal  cord.  But  experiments 
have  shown  that  they  are  not  the  only  cortico-spinal  paths  nor  even 
the  most  important  in  many  animals,  for  the  paralysis  which  results 
from  their  section  is  .soon  recovered  from  in  most  animals,  whereas 
that  resulting  from  section  of  the  anterior  column  and  adjacent  part  of 
the  lateral  column  may  be  more  marked  and  permanent.  In  man  it 
appears  to  be  the  finer  and  more  delicate  movements  which  are 
permanently  lost  when  the  pyramidal  tract  is  affected  by  disease. 

2.  Tract  of  Loewenthal. — Besides  the  pyramidal  tracts  there  are 
four  other  "descending"  tracts  of  fibres  in  the  antero-lateral  column. 
One  of  these  (the  anicro-lateral  descending  tract  or  tract  of  Luewentluil, 
figs.  435,  436,  3)  lies  on  the  side  of  the  anterior  median  fissure,  and 
extends  along  the  margin  of  the  cord  in  the  "root"  zone,  even 
reaching  the  anterior  part  of  the  lateral  column.  These  fibres  are 
continued  down,  chiefly  from  the  posterior  longitudinal  bundle  (vestibulo- 


364 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fig.  437.— Diagram  showing  the  course  of  the  tr.\cts  of  Flkchsig  and 
of  gowers  in  the  spinal  cord  and  their  continuations  to  the  cere- 
bellum, corpora  quadrigemina,  thalamus  and  cortex  cerebri. 

a,  posterior  root-fibres  ;  h,  tract  of  Flechsig,  passing  at  b',  by  the  restiform  body  to  the 
cerebellar  vermis ;  c,  tract  of  Gowors  ;  rf,  passage  of  most  of  its  fibres  along  the 
superior  peduncle  to  the  cerebellum  ;  c,  fibres  to  the  corpora  quadrigemina,  «' ;  /, 
others  to  the  thalamus  ;  g,  fibres  from  thalamus  to  cerebral  cortex. 


THE   SPINAL  CORD.  365 

^inal  fiJyres)  of  the  nicdulhi  o])longatti  aivd  pons  Varolii,  partly  from 
other  sources  which  will  l)e  afterwards  referred  to.  They  end  by 
arborisations  in  the  anterior  horn.  Similar  arborisations  pass  from 
the  posterior  lotii^itudinal  bundle  to  the  nuclei  of  the  motor  cranial 
nerves.     This  tract  is  mainly  uncrossed. 

3.  Rubrospinal  trad. — Another  "descending"  tiact  in  the  antero- 
lateral column  lies  just  in  front  of  the  crossed  pyramidal  tract.  This 
is  the  prepijramidal  or  ruhrospinal  trad  (figs.  435,  436,  .4);  its  fibres 
end  by  arborising  in  the  grey  matter  of  the  middle  of  the  crescent ; 
the  situation  of  its  cells  of  origin  is  the  red  nucleus  of  the  tegmentum 
in  the  mid-brain.  This  tract  is  also  known  as  Monukow's  trad. 
Some  of  its  fibres  are  stated  to  be  derived  from  cells  in  the  reticular 
formation  of  the  pons  and  medulla  oblongata. 

4.  Tedu-spimd  fibres. — Intermingled  with  the  fibres  of  the  rubro- 
spinal tract  (but  far  fewer  in  number  in  man)  are  fibres  derived 
from  the  quadrigeminal  bodies  of  the  opposite  side.  These  fibres 
form  a  part  of  the  tcdo-spinal  trad.  Another  part  of  this  tract  passes 
into  the  anterior  column  of  the  cord  in  the  tract  of  Loewenthal 
above  mentioned. 

5.  Olivospinal  trad. — Lastly  a  small  triangular  group  of  "descend- 
ing" fibres  traceable  from  the  neighbourhood  of  the  olive  in  the 
medulla  oblongata,  and  passing  down  the  cervical  cord  in  the 
anterior  part  of  the  lateral  column  (fig.  435,  Sa),  (the  exact  origin 
and  destination  of  the  fibres  is  unknown)  is  termed  the  bundle  of 
Hehceg  or  olivosjmial  trad. 

Ascending  tracts  of  the  antero-lateral  column. — 1.  Trad  of 
Fledisig. — This  is  a  well-marked  tract,  which  is  however  only  distinct 
in  the  cervical  and  dorsal  regions,  where  it  lies  external  to  the 
crossed  pyramidal  tract.  It  consists  of  large  fibres  which  are  derived 
from  the  cells  of  Clarke's  column  (fig.  434,  /)  and  which  pass  up  into 
the  cerebellar  vermis  by  way  of  the  inferior  peduncle  of  the  same  side 
{dorsal  spina-cerebellar  bundle  or  dired  cerebellar  tract  of  Flechsig,  fig.  434; 
figs.  435,  436,  9 ;  437,  b,  U). 

2.  Trad  of  Gowerc. — This  is  situated  more  anteriorly,  lying  in 
front  of  the  crossed  pyramidal  and  direct  cerebellar  tracts  in  the 
luml)ar  region  ;  while  in  the  dorsal  and  cervical  regions  it  forms  a 
narrow  band  of  fibres  curving  round  close  to  the  external  surface 
of  the  cord,  and  extending  even  into  the  anterior  column.  It  was 
termed  the  aidcro-lutcral  ascending  trad  by  Gowers  (figs.  43r),  436,  10). 
Its  fibres  are  intermingled  with  those  of  the  antero-lateral  descend- 
ing tract.  Most  of  the  fibres  of  the  tract  of  Gowers  are  con- 
nected  with    the  vermis   of  the  cerebellum,  constituting  the  ventral 


366  THE   ESSENTIALS  OF   HISTOLOGY. 

spino-cerebellar  hindle,  which  passes  to  that  organ  over  and  parallel 
with  the  superior  cerebellar  peduncle  (fig.  437).  According  to  Van 
Gehuchten,  confirmed  by  Collier  and  Buzzard,  the  tract  of  Gowers 
gives  oflp  a  few  fibres  to  enter  the  opposite  cerebellar  hemisphere 
by  the  middle  peduncle. 

Some  of  the  fibres  of  the  antero-lateral  ascending  tract  {spino-tedal 
fibres)  are  continued  up  to  the  corpora  quadrigemina.  Others  pass 
into  the  tegmentum  of  the  crus  cerebri,  where  they  can  be  traced  as 
far  as  the  lower  part  of  the  thalamus  (spino-thalamic  fibres). 

The  cells  from  which  the  fibres  of  Gowers'  tract  take  origin  are 
not  certainly  known,  but  it  is  probable  that  they  are  cells  situated 
in  the  middle  and  posterior  parts  of  the  grey  crescent,  partly  on 
the  same  but  chiefiy  on  the  opposite  side  of  the  cord.  The  latter  is 
almost  certainly  the  case  with  the  cells  from  which  the  spino-thalamic 
fibres  arise. 

3.  Trad  of  Lissauer. — Lastly,  there  is  another  small  tract  of  fibres 
which  undergoes  degeneration  above  the  point  of  section.  This  is 
the  marginal  bundle  of  Lissauer  (marked  M  in  fig.  434).  It  is  formed 
by  fine  fibres  from  the  posterior  roots. 

Other  portions  of  the  antero-lateral  columns  near  the  grey  matter 
which  are  difterentiated  by  the  method  of  Flechsig  are  probably  short 
tracts  uniting  adjacent  portions  of  the  grey  matter  of  the  cord. 

Proprio-spinal  or  endogenous  fibres  of  the  antero-lateral  column. — 
Sherrington  has  shown  that  in  the  dog  the  lateral  column  in  the  dorsal 
region  of  the  cord  contains  a  certain  number  of  long  fibres  which  take 
origin  in  the  cervical,  dorsal  and  upper  lumbar  segments  and  are 
traceable  down  to  the  lumbo-sacral  enlargement.  These  must  serve ' 
to  convey  excito-refiex  impulses  from  the  upper  to  the  lower  parts  of 
the  body.  Probably  similar  fibres  arise  all  along  the  cord  from  the 
cells  of  the  lateral  column  and  pass  upwards  as  well  as  downwards. 

A  tract  of  endogenous  fibres  has  been  observed  in  man  close  to  the 
anterior  median  fissure  lying  amongst  the  fibres  of  the  direct  pyramidal 
tract.     This  is  known  as  the  anterior  sulco-marginal  trad  of  Marie. 

The  antero-lateral  column  contains  also  many  endogenous  fibres, 
both  ascending  and  descending,  derived  from  cells  in  the  grey  matter 
of  the  cord,  which  have  only  a  short  course,  serving  to  connect 
adjacent  segments. 

GREY   MATTER   OF   CORD. 

The  nerve-cells  which  are  scattered  through  the  grey  matter  are 
in  part  disposed  in  definite  groups.  Thus  there  are  several  groups 
of  large  multipolar  nerve-cells  in  the  anterior  horn  in  the  cervical  and 


THE   SPINAL  CORD. 


367 


in. 


VII. 


VIII. 


Fig.  488. — Diagram  of  sections  of  the  spin.al  coed  of  the  monkey  show- 
ing THE  POSITION  OF  DEGENERATED  TRACTS  OF  NERVE-FIERES  AFTER 
SPECIFIC    LESIONS    OF    THE   CORD    ITSELF,     THE   EFFERENT   NERVE-ROOTS    AND 

OF  THE  MOTOR  REGION  OF  THE  CEREBRAL  CORTEX.  (The  degenerations  are 
shown  by  the  method  of  Marchi.)  The  left  side  of  the  cord  is  at  the 
reader's  left  hand. 

I.  Degenerations  resulting  from  extirpation  of  the  motor  area  of  the  cortex  of  the  left 

cerebral  hemisphere. 

II.  Degenerations  produced  by  section  of  the  posterior  longitudinal  bundles  in  the  upper 
part  of  the  medulla  oblongata. 

III.  and  IV.  Result  of  section  of  posterior  roots  of  the  first,  second,  and  third  lumbar 
nerves  on  the  right  side.  Section  III.  is  from  the  segment  of  cord  between  the  last 
thoracic  and  first  lumbar  roots  ;  section  IV.  from  the  same  cord  in  the  cervical  i-ogion. 

V.  to  VIII.  Degenerations  re.sulting  from  (right)  semi-section  of  the  cord  in  the  upper 
thoracic  region.  V.  is  taken  a  short  distance  above  the  level  of  section  ;  VI.,  higher  up 
the  cord  (cervical  region) ;  VII. ,  a  little  below  the  level  of  section  ;  VIII. ,  lumbar  region. 


368 


THE   ESSENTIALS  OF   HISTOLOGY 


Sacr.l 


Sacr.3 


Fig.  439.— Diagram  of  sections  of  human  spinal  cord  at  different 
LEVELS.     (Edinger. ) 
The  names  refer  to  the  origin  of  the  corresponding  nerve  roots.     The  relative  shape  and 
size  of  the  cord  and  grey  matter,  and  the  relative  amounts  of  gi-ey  and  white  matter, 
and  the  principal  cell-gi-oups  are  shown. 


THE   SPINAL  CORD 


369 


lumbar  enlargements  (fig.  435),  although  in  other  regions  of  the  cord 
the  number  of  groups  in  this  situation  is  reduced  to  two,  a  mesial 
and  a  lateral.  The  larger  groups  in  the  enlargements  correspond  with 
segments  of  the  limb  (Van  (Tehuchten) ;  thus  there  appear  to  be 
groups  associated  with  foot,  leg,  and  thigh,  and  with  hand,  arm,  and 
shoulder  movements  respectively.  The  groups  from  which  the  motor 
nerves  to  the   shouldei'  and   arm   muscles  arise  appear  in   somewhat 

b  a     u     t      ? 


Fig.   440.— Diagram  showing   the   probable   relations  of   some   of   the 
CELLS  OF  the  CORD  TO  THE  WHITE  COLUMNS.      On  the  left  side  the  col- 
laterals from  the  fibres  of  the  white  columns  are  shown  passing  into  the 
grey  matter.     (Cajal.) 
a,  b,  fibres  of  posterior  column  sending  collaterals  into  the  grey  matter ;  c,  d,  fibres  of 
posterior  root  entering  posterior  column  ;  c,  /",  collaterals  passing  from  lateral  and 
anterior  columns  into  grey  matter  ;  .a,  h,  i,  fibres  of  white  commissure ;  j,  anterior 
root-fibre  springing  from  Ic,  cell  of  anterior  lioi-n  ;  I,  m,  n,  other  cells  of  grey  crescent 
sending  their  axons  into  the  white  matter  ;  o,  axon  of  cell  of  Clarke's  column  passing 
into  the  dorsal  cerebellar  tract;  p,  axon  of  cell  of  substantia  gclatinosa ;  g,  fibre  of 
dorsal  cerebellar  tract ;  r,  fibre  of  posterior  root  passing  to  tract  of  Lissauer  ;  s,  t,  cells 
of  substantia  gelatinosa  ;  u,  cell  of  Clarke's  column. 

higher  segments  of  the  cervical  cord  than  those  belonging  to  the  hand 
muscles.  The  same  holds  good,  mutatis  mutandis,  for  the  lumbar  cord 
in  relation  to  the  leg  and  foot.  Further,  the  larger  groups  show 
subdivisions  which  may  be  related  to  particular  movements,  i.e.  to 
particular  groups  of  muscles.  In  the  case  of  the  diaphragm  there  is  a 
special  cell-group  or  cell-column  in  the  cervical  cord  (anterior  horn) 
from  which  the  fibres  of  the  phrenic  nerve  arise,  so  that  in  this  case 
a  cell-group  is  set  apart  for  a  special  muscle. 

The  axis-cylinder  processes  of  the  anterior  horn  cells  mostly  pass  out 
into  the  corresponding  anterior  nerve-roots  (fig.  436,  m ;  fig.  440,  j), 
but  a  few  send  their  axons  to  the  anterior  column  of  the  opposite  side 
through  the  white  commissure  (fig.  440,  m)  or  to  the  anterior  or  lateral 
column  of  the  same  side  {I,  n).     It  is  noteworthy  that  in  birds  a  few 

2a 


370 


THE   ESSENTIALS   OF  HISTOLOGY. 


cells  of  the  anterior  horn  send  their  axons  into  the  posterior  roots.  A 
well-marked  group  of  large  rounded  nerve-cells,  best  marked  in  the 
thoracic  region,  lies  at  the  base  of  the  posterior  horn  (nucleus  of  Stilling, 
Clarke's  column,  fig.  434,  /;  fig.  435,  d ;  fig.  440,  u).  The  cells  of 
Clarke's  column  send  their  axis-cylinder  processes  into  the  dorsal 
cerebellar  tract  (Mott),  and  if  this   tract  V)e  cut  experimentally,  the 


Fig    441.— From  a  LOxcrruDiNAL  sec- 

TIOX   OF   SPIXAL    CORD,    SHOWING    THE 
ENTRANCE  OF  POSTERIOR  ROOT-FIBRES. 

(Cajal.) 
A,  A,  fibres  entering  the  postero-lateral 
column,  and  bifurcating  into  an  ascending 
and  descending  division  ;  B,  C,  collaterals 
passing  from  them  into  the  grey  matter ; 
E,  other  fibres  of  the  posterior  white 
columns  also  giving  off  collatei-als. 


Fig.  442.  —  Arbori.sation  of  col- 
laterals FROM  THE  POSTERIOR  ROOT- 
FIBRES  AROUND  CELLS  IN  THE  POS- 
TERIOR      HORN       OF       GREY       MATTER. 

(Cajal.) 
A,  fibres  of  posterior  column  derived  from 
posterior  root ;  B,  collaterals  ;  C,  D,  nerve- 
cells  in  grey  matter  surrounded  by  the 
arborisations  of  the  collaterals ;  E,  an 
aiborisation  shown  separately. 


large  cells  of  Clarke's  column  on  the  same  side  below  the  section 
undergo  Xissl  degeneration  and  eventually  atrophy.  There  are,  how- 
ever, a  few  small  cells  with  short  axons  in  Clarke's  column  which  do 
not  undergo  this  change. 


THE   SPINAL  CORD.  371 

Another  group  is  seen  on  the  outer  side  of  the  grey  matter  lying  in 
a  projection  which  is  sometimes  known  as  the  lateral  horn  {lateral 
cell-cohuiin,  inter  media-lateral  column,  figs.  434,  d ;  435,  i).  This  is  most 
distinct  in  the  dorsal  I'ogion  (as  far  up  as  the  second  thoracic  segment). 
The  axons  from  its  cells  for  the  most  part  leave  the  cord  along  with 
the  anterior  roots,  and  probahly  furnish  the  outgoing  visceral  and 
vascular  fibres.  Another  group  {middle  cell-column)  lies  in  the  middle 
of  the  crescent  (fig.  434,  e).  The  cells  of  the  posterior  horn  (cj)  are 
very  numerous  hut  are  not  collected  into  definite  groups.  Those  of 
the  substantia  gelatinosa  of  Rolando  send  their  nerve-fibre  processes 
partly  into  the  lateral,  partly  into  the  adjacent  posterior  columns 
(fig.  440,  s,  t). 

The  cells  which  seud  their  axons  into  the  adjacent  parts  of  the  white 
columns  but  not  into  any  sjDecial  tract  are  sometimes  termed  the  "  cells  of 
the  white  columns." 

Connection  of  nerve-roots  with  spinal  cord. — The  anterior  roots 
leave  the  anterior  horn  in  a  nunil)er  of  bundles.  Most  of  their  fil^res 
are  directly  continued  from  the  nerve-cells  in  the  anterior  and  lateral 
horns,  and  according  to  Golgi  in  part  also  from  cells  in  the  posterior 
horn.  These  cells,  from  which  the  anterior  root-fibres  arise,  are 
surrounded  by  an  interlacement  of  ramified  nerve-endings,  which 
are  derived  from  various  sources,  especially  the  axons  of  cells  of  the 
posterior  horn,  from  collaterals  of  the  posterior  root-fibres  (see  below), 
and  from  those  of  the  fibres  of  the  adjacent  white  columns. 

The  fibres  of  the  posterior  roots  originate  in  the  cells  of  the  posterior 
root  ganglia  and  pass  into  the  posterolateral  column   (see  diagram, 
fig.  436),  but  the  smallest  fibres  enter  the 
marginal  bundle  of  Lissauer,   and  some 
pass  directly  into  the  posterior  horn  of 
grey    matter.       On    entering    the    spinal 
cord  the  fibres  bifurcate   (fig.   441),  one 
branch  passing  upwards,  the  other  down- 
wards.     Both  from  the  main  fibre  and 
from  its  branches  collateral  fibres  pass  at 
frec^uent  intervals  into  the  grey  matter, 
and  end  in  arborisations  of  fibrils  which      ^'^-^if'-^^^Z  ?HE™fpZ. 
envelop     the     nerve-cells    both     of    the         cord  of  a  child,  showing 

,  „       ,  ■  y  ,n  ITS    CILIATED    EPITHELIUM   AND 

posterior  and  of  the  anterior  horn  (hg.  the  surrounding  central 
442)  and  in  the  dorsal  region  the  cells  of  Su  """■  ^^^""^^'^^^^^  "'^' 
Clarke's  column   and  those  of  the  inter- 

medio-lateral  tract.  Many  of  the  main  fibres  also  ultimately  end  in  a 
similar  manner  in  the  grey  matter,  some  after  a  short  course  only,  but 


372 


THE   ESSENTIALS   OF  HISTOLOGY. 


Fig.   444.— Part  of  epithelium  of  central  canal  of  new-born   child, 

STAINED    BY    GOLGl'S    METHOD.       (Sobottfl.)       X    120. 
ep,  epithelium  ;  ng,  neuroglia  celLs  in  adjacent  grey  matter. 


I  Fig.  445. — Section  of  cord  of  embryo,  showing  some  of  the  ependyma  cells 

DETACHED   AND  BECOMING  CONVERTED  INTO  NEOROGLIA-CELLS.      (L^nllOSSek.) 


THE   SPINAL  CORD.  373 

others  after  a  longer  course.  But  a  considerable  number  of  fibres  pass 
upwards  in  the  postero-lateral  and  postero-mesial  columns  (in  the  latter 
especially  those  of  the  lower  spinal  nerves),  until  they  arrive  at  the 
medulla  oblongata,  where  they  end  in  terminal  arborisations  around 
the  cells  of  the  nucleus  gracilis  and  nucleus  cuneatus. 

The  central  canal  of  the  spinal  cord  is  lined  by  columnar  ciliated 
epithelium-cells  {ependyma),  which  arc  surrounded  by  a  quantity  of 
neuroglia.  The  cells  are  best  seen  in  the  spinal  cord  of  animals 
and  in  the  child  (figs.  443,  444) ;  in  the  human  adult  they  have 
frequently  become  proliferated,  and  their  cilia  are  no  longer  visible. 
In  the  early  embryo  their  fixed  extremities  extend  through  the  whole 
thickness  of  the  cord  to  reach  the  pia  mater.  This  condition  is 
permanent  in  the  cord  of  many  of  the  lower  vertebrata. 

Blood-vessels  of  the  spinal  cord. — The  blond-supply  of  the  grey  matter 
is  derived  mainly  from  a  series  of  arterioles,  which  come  oil'  from  the 
mesially- situated  anterior  spinal  artery,  pass  into  the  anterior  median 
fissure,  and  at  the  bottom  of  this  divide  each  into  two  branches,  one  for  the 
grey  matter  of  each  lateral  half  of  the  cord.  In  the  grey  matter  is  a  very 
close  capillary  plexus  which  is  supplied  not  alone  by  the  vessels  just 
mentioned,  but  also  by  small  arterioles,  which  converge  from  the  small 
arteries  of  the  pia  mater,  passing  through  the  white  matter,  and  supplying 
this  as  they  pass  through  it.  These  arterioles  are  branches  of  the  above- 
mentioned  anterior  spinal  artery  and  of  the  posterior  spinal  arteries  (which 
run  on  each  side  along  the  line  of  the  posterior  roots).  The  capillary 
plexus  of  the  white  matter  is  far  less  dense  than  that  of  the  grey  matter. 
It  forms  longitudinal  meshes. 

The  veins  of  the  spinal  cord  accompany  the  arteries.  Two  longitudinal 
venous  vessels,  accompanying  corresponding  anastomotic  arterioles,  are  seen, 
one  on  either  side  of  the  central  canal,  in  most  transverse  sections  of  the 
cord. 


374  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSON    XLI. 

THE  MEDULLA    OBLONGATA. 

Sectioxs  of  the  medulla  oblongata  (made  in  the  same  way  as  with  the  spinal 
cord)  :  (a)  at  the  level  of  the  decussation  of  the  pyramids,  (6)  just  above  the 
decussation,  (c)  opposite  the  middle  of  the  olivary  body,  and,  (c/)  either 
through  the  uppermost  part  of  the  olivary  body,  or  just  above  it. 


The  brain  consists  of  three  great  morphological  divisions  associated 
with  the  three  primary  cerebral  vesicles  of  the  embryo;  they  are 
termed  respectively  the  hind-brain,  mid-brain,  and  fore-brain. 

The  hind-brain  is  formed  of  the  parts  around  the  fourth  ventricle, 
viz.,  the  medulla  oblongata  or  spinal  bulb  (myelenceplialon),  and  above 
this  the  pons  Varolii  with  the  cerebelhim  (metencephalon)  :  the  region 
of  the  corpora  quadrigemina  forms  the  mid-brain  (mesencephalon) ; 
the  parts  immediately  above  that  region,  and  centring  around  the 
third  ventricle,  including  the  optic  thalami,  form  the  thalamencephalon  ; 
and  the  corpora  striata  and  cerebral  hemispheres  constitute  the  telen- 
cephalon. 

The  structure  of  the  medulla  oblongata  or  spinal  bulb  can  best 
be  made  out  by  the  study  of  a  series  of  sections  taken  from  below 
upwards,  and  by  tracing  in  these  the  changes  which  occur  in  the 
constituent  parts  of  the  spinal  cord,  taking  note  at  the  same  time 
of  any  parts  which  may  be  superadded. 

A  section  through  the  region  of  the  decussation  of  the  pyramids 
(fig.  446)  has  much  the  same  form  as  a  section  through  the  upper 
part  of  the  spinal  cord,  and  most  of  the  structures  of  the  cord  can 
be  easily  recognised.  A  considerable  alteration  of  the  grey  matter 
is,  however,  produced  by  the  passage  of  the  large  bundles  of  the 
crossed  pyramidal  tract  from  the  lateral  column  of  the  spinal  cord 
on  each  side  through  the  root  of  the  anterior  horn  and  across  the 
anterior  median  fissure  to  the  opposite  anterior  column  of  the 
medulla  oblongata,  where,  together  with  the  fibres  of  the  direct 
pyramidal  tract,  they  constitute  the  prominent  mass  of  white  fibres 
which  is  seen  on  the  front  of  the  bulb,  on  each  side  of  the  middle 
line,  and  which  is  known  as  the  pyramid.  By  this  passage  of  fibres 
through  the  grey  matter  the  tip  of  the  anterior  horn  is  cut  off  from 


THE   MEDULLA   OBLONGATA. 


375 


the  rest  and  becomes  pushed  as  it  were  to  the  side ;  part  of  it 
appears  as  an  isolated  mass  or  masses  of  grey  matter,  one  of  which 
becomes  known  as  the  lateral  nucleus.  In  sections  just  above  the 
decussation  of  the  pyramids  a  wavy  mass  of  gi-ey  matter  makes  its 


funiculus  gracili.H 
post,  modiaii  fissure  - 


,/     '^ 


funiculus  cuneatus 


nucleus  gracilis    ^  *;■ 


7^^^' 


_.4 


r./ll  rj 


desc.  Vth 4r 

bundle  from  fun.  cun.       -  '  " '  ' — 
subst.  gelat.  Rol.- 


tract  of  Flechsig 


pyramidal  ti-act 

bundle.' 


\  :■ 


*: 


decussation  of 

pyramids 


anterior  horn 


\ 


ant.  median  fissure       ■., 


pyi-amid 


/ 


Fig.  446.— Section  aceoss  the  lower  part  of  the  medulla  oblongata  in 

THE     region    of    THE     DECUSSATION    OF    THE     PYRAMIDS.        (Magnified    65 

diameters.) 

appearance  on  the  lateral  aspect  of  each  pyramid,  corresponding 
with  a  prominence  on  the  surface  which  is  known  as  the  olive.  The 
wavy  or  plicated  grey  matter  is  termed  the  olivary  nucleus  (figs.  447 
to  449). 

The  pyramids  (anterior  pyramids)  of  the  medulla  oblongata  are 
formed  of  fibres  which  originate  in  the  motor  region  of  the  cerebral 
cortex,  and  which  can  be  traced  from  the  axons  of  large  cells  in  the 
grey  matter  of  that  cortex  through  the  white  matter  of  the  hemisphere, 
through  the  middle  third  or  more  of  the  internal  capsule  and  crusta, 
through  the  pyramid  bundles  of  the  pons  Varolii  and  into  these 
structures  (pyramids)  of  the  bulb.  As  we  have  just  seen,  they  pass 
at   the   lower   limit   of  the   bulb  chiefly  to  the  opposite  or  crossed 


376 


THE   ESSENTIALS   OF   HISTOLOGY. 


lateral  column  of  the  cord,  but  partly  to  the  lateral  column  of  the 
same  side,  and,  in  man  and  anthropoid  apes,  partly  to  the  anterior 
column.  They  collectively  constitute  the  p/fvcmiidal  trad,  which  is 
smaller  in  the  medulla  oblongata  than  in  the  pons  Varolii,  since 
many  of  its  fibres  have  left  the  main  tract  whilst  within  the  pons 
and  have  passed  across  the  middle  line  towards  the  grey  matter  on 


post,  median  fissure 

nucleus  gracilis — 
funiculus  cuneatus 

nucleus  cuneatus' 


desc.  root  of  otl 

central  canal 

substantia  Roland:' 

central  fibres  of  Vtl 

int.  arcuate  fibre; 

tract  of  Fleclisig'^ 

tract  of  Gowersv 


raphe 

accessory  oliv.  nucl. 

siliqua  oliva; 

olivary  nucleus' 


pyramid 


arcuate  nucleus^ 


Fig.  447. — Section  taken  immediaj'elt  above  the  decussation  of  the 
PYRAMIDS.     (Magnified  6g  diameters.) 


the  dorsal  aspect  of  the  pons  and  medulla  oblongata.  Sometimes 
such  a  bundle  of  fibres,  after  passing  towards  the  sensory  nuclei  in 
the  lateral  part  of  the  medulla  oblongata,  does  not  end  in  them,  but 
again  comes  ventral-wards  and  joins  the  main  or  central  part  of  the 
tract  near  its  decussation  (Imndle  of  Pick). 

It  is  not  a  little  remarkable  that  although  the  fibres  of  the  pyramidal  tract 
give  off  numerous  collaterals  to  the  grey  matter  of  the  cerebral  cortex,  the 
basal  ganglia  of  the  cerebrum,  the  substantia  nigra  of  the  mid-brain,  the 
nuclei  pontis  of  the  pons  Varolii,  and  the  base  of  the  posterior  horn  of 
the  spinal  cord,  no  collaterals  are  seen  to  leave  them  in  their  course  through 
the  medulla  oblongata,  except  a  very  few  to  the  olivary  nuclei.  Various 
observers  have  described  collaterals  and  terminations  of  the  pyramidal  fibres 


THE   MEDULLA   OBLONGATA.  377 

as  passing  to  the  motor  nuclei  of  the  cranial  nerves  as  well  as  to  the  anterior 
horns  of  the  spinal  cord,  but  statements  to  this  effect  must  be  received  with 
caution  for  although  current  in  most  text-books,  they  have  not  been  sub- 
stantiated by  accurate  observations.  It  is  certain  that  most  if  not  all  of  the 
fibres  of  the  pyramidal  tract  end  not  in  the  ventral  but  in  the  dorsal  part 
of  the  grey  matter  of  the  cord. 

A  change  also  occurs  in  the  posterior  horn  in  consequence  of  the 
increased  development  of  the  posterior  column  of  white  matter.  This 
causes  the  posterior  horns  to  be  pushed  towards  the  side,  the  V  which 
they  form  with  one  another  being  thus  opened  out ;  at  the  .same  time 
the  tip  of  the  hoi'u  swells  out  and  causes  a  prominence  upon  the  surface 
of  the  medulla  oblongata,  which  is  known  as  the  tubercle  of  Rolando. 
Its  grey  matter  forms  the  prolongation  of  the  sensory  nucleus  of  the 
fifth  nerve.  On  its  outer  side  and  partly  embracing  it  is  a  bundle  of 
fibres  seen  in  every  section  of  the  medulla  oblongata,  and  traceable  up 
to  the  pons  Varolii.  This  is  the  inferior  or  descending  root  of  the  fifth 
nerve — formerly  kno^vn  as  the  "ascending"  root.  Its  fibres  extend 
down  as  far  as  the  upper  cervical  region  of  the  spinal  cord.  Grey 
matter  also  soon  becomes  formed  within  the  upward  prolongations  of 
the  gracile  funiculus  (postero-mesial  column),  and  of  the  cuneate 
funiculus  (postero-lateral  column)  appearing  at  first  as  thin  strands  in 
the  middle  of  the  columns,  but  rapidly  increasing  in  thickness  so  as 
eventually  to  occupy  almost  the  whole  of  them,  and  forming  the 
nucleus  gracilis  and  the  micleus  cuneatus  respectively. 

It  is  in  these  nuclei  that  the  fibres  of  Goll's  and  Burdach's  tracts, 
which  are  continued  up  from  the  posterior  columns  of  the  spinal  cord, 
find  their  ultimate  ending  in  complicated  arborisations  amongst  the 
cells  of  the  nuclei.  These  nuclei  do  not,  however,  receive  all  the 
ascending  branches  of  the  posterior  root  fibres,  for  a  considerable 
number  of  these  have  already  disappeared  by  entering  the  grey 
matter  of  the  cord,  in  which  they  also  end  by  arborisation 
amongst  its  cells.  The  cells  of  the  nucleus  gracilis  and  nucleus 
cuneatus  are  small  or  of  moderate  size  with  long  dendrons.  Their 
axons  pass  as  internal  arcuate  fibres  through  the  reticular  formation 
into  the  inter-olivary  layer,  cross  the  median  raphe  dorsal  to  the 
pyramids  (fig.  447),  and  then  turn  upwards,  constituting  the  tract  of 
the  fillet.  This  tract,  which  in  its  lowest  part  is  thus  formed  by  the 
nerve-fibres  which  belong  to  the  second  relay  (or  second  neurones) 
of  one  of  the  sensory  spinal  paths,  is  reinforced  in  the  higher  regions 
of  the  medulla  oblongata  and  in  the  pons  by  fibres  derived  from 
cells  of  the  sensory  nuclei  of  the  cranial  nerves.  The  majority  of 
its  fibres  end  in  the  lateral  nucleus  of  the  thalamus,  but  some  pass 
to  both  the  anterior  and  posterior  corpora  quadrigemina. 


378 


THE   ESSENTIALS  OF   HISTOLOGY. 


According  to  Van  Gehuchten  the  fibres  of  the  fillet  which  are  derived  from 
the  nucleus  cuneatus  lie  dorsally  to  those  which  are  derived  from  the  nucleus 
gracilis. 

The  continuation  of  the  central  canal  of  the  spinal  cord  is  still  seen  in 
the  lower  medulla  oblongata  (figs.  446,  447),  but  it  comes  nearer  to  the 
posterior  surface  and  eventually  opens  out  at  the  point  of  the  calamus 
scriptorius  of  the   4th   ventricle   (fig.   448).     The  grey  matter  which 


nucleus  gracilis 


funiculus  cuneatus' 
nucleus  cuneatus 


fasciculus  solitarius, 
dorsal  nucleus  of  Xth 
desc.  root  of  Vth 
nucleus  of  Xlltli, 

subst.  gelat.  Roland 

traot  of  Flechsig. 

int.  arcuate  fibres 

rubro-spinal  tract 

issuing  fibres  of  Xllth, 

tract  of  Gowers 


siliqua  olivft' 
olivary  nucleus 

ext.  arcuate  fibres 


pyrau  1  id 


arcuate  nucleus 


Fig.  448. — Section  across  the  medulla  oblongata  at  the  point  of  the 
CALAMUS  SCRIPTORICS  OF  THE  4th  VENTRICLE.     (Magnified  65  diameters. ) 

surrounds  it  contains  two  well-marked  groups  of  nerve-cells ;  tlie 
anterior  (ventral)  of  these  is  the  lower  part  of  the  nucleus  of  the 
hypoglossal  or  twelfth  nerve,  the  posterior  (dorsal),  with  smaller  cells, 
that  of  the  vago-accessori/  or  tenth  and  eleventh.  But  most  of  the  grey 
matter  of  the  crescent  becomes  broken  up,  by  the  passage  of  bundles 
of  nerve-fibres  through  it.  into  a  reticular  formation  the  production  of 
which  is  already  foreshadowed  in  the  upper  part  of  the  spinal  cord. 
Instead  of  the  comparatively  narrow  isthmus  which  joins  the  two 
halves  of  the  spinal  cord,  a  broad  raphe  now  makes  its  appearance ; 


THE   MEDULLA   OBLONGATA. 


379 


this    is    formed    of  ol)li([uely    and    antero-posteriorly    coursing    fibres, 
together  with  some  grey  matter  containing  nerve-cells. 

In  the  section  at  about  the  middle  of  the  olive  (fig.  449),  it  will  be  seen 
that  a  marked  change  has  been  produced  in  the  form  of  the  medulla 
oblongata  and  the  arrangement  of  its  grey  matter,  by  the  opening  out 
of  the  central  canal  into  the  fourth  ventricle.     This  causes  the  grey 


vestibular  nucleus 

<lesc.  fibres  of  vestibular 
tlorsal  nucleus 

of  Xtl 

fasciculus  solit. 
restiform  body 
nucl.  of  Xlltij 

subst.  gclat. 

desc.  root  of  Vth 

subst.  gelat 

int.  arc.  fibres 

and  nucl.  amb. 

issuing  fibres  of 

Xtb 


issuing  fibres  oi 
Xllth 

raphe 


siliqua  olivtt;,       

hilus  olivse, 

olivary  nucleu 

ext.  arcuate  fibre* 


5^r' 


arcuate  nucleus 


m 


Fig.  449. — Section  across  the  jiedulla  oblongata,  .at  about  the  middle 
OF  THE  olivary  BODY.     (Magnified  6^  diameters.) 


matter  which  lower  do^^'Tl  surrounded  the  central  canal  to  be  now 
spread  out  at  the  floor  of  that  ventricle,  and  the  collections  of 
nerve-cells  from  which  the  hypoglossal  and  A'agus  nerves  respectively 
arise,  now,  therefore,  lie  in  a  corresponding  situation  near  the 
ventricular  floor.  At  this  level  the  outer  small-celled  group  which 
corresponds  with  the  nucleus  of  the  spinal  accessory  in  the  lower  part 
of  the  bulb  has  become  the  dorsal  nucleus  of  the  vagus  or  tenth  nerve, 
and    yet   higher   up    the    dorsal   nucleus   of  the   ninth   nerve   or   glosso- 


380  THE   ESSENTIALS   OF   HISTOLOGY. 

pharyngeal.  The  nerve -bundles  of  the  roots  of  these  nerves  can  be 
seen  in  some  of  the  sections  (fig.  449)  coursing  through  the  thickness 
of  the  bulb  and  emerging,  those  of  the  hypoglossal  just  outside  the 
pyramids,  those  of  the  vagus  at  the  side  of  the  medulla  oblongata. 

The  posterior  part  of  the  section  is  chiefly  occupied  by  the  grey 
matter  of  the  floor  of  the  fourth  ventricle,  and  by  fibres  which  are 
passing  obliquely  upwards  and  outwards  towards  the  cerebellum, 
forming  its  inferior  crus  (restiform  body).  The  grey  matter  forming 
the  nucleus  of  the  funiculus  gracilis  and  of  the  funiculus  cuneatus  has 
now  almost  disappeared,  but  in  place  of  them  and  near  the  outer  part 
of  the  floor  of  the  fourth  ventricle  are  seen  some  masses  of  grey  matter 
with  a  number  of  bundles  of  nerve-fibres  amongst  them.  The  grey 
matter  is  the  lower  part  of  the  principal  nucleus  of  the  vestibular 
nerve  (see  p.  38 7 j,  and  the  white  bundles  are  formed  of  descending 
branches  of  the  fibres  of  that  nen-e.  Below  these  structures  is  the 
descending  root  of  the  5th,  with  its  descending  nucleus  mesial  to  it. 

The  anterior  part  of  the  section  is  occupied  in  front  by  the  pj-ramid, 
and  behind  this  by  a  reticular  formation  {reticularis  alha),  composed  of 
longitudinally  coursing  bundles  of  fibres  belonging  mainly  to  the  tract 
of  the  fillet  and  to  the  dorsal  and  ventral  (posterior  and  anterior)  longi- 
tndinal  bundles,  interlaced  with  internal  arcuate  fibres  that  are  passing 
across  the  raphe  from  the  nuclei  of  the  contralateral  posterior  columns 
into  the  fillet,  and  from  the  opposite  olive  into  the  restiform  body. 

The  middle  portion  of  the  section  consists  for  the  most  part 
of  a  similar  reticular  formation,  but  with  more  grey  matter  and 
nerve-cells  {reticularis  grisea).  This  is  a  development  of  the  formatio 
reticularis  of  the  cervical  cord,  and  the  longitudinally  coursing 
white  bundles  in  it  are  probably  association  fibres,  derived  from 
cells  in  the  upper  part  of  the  cord.  On  the  other  hand  the 
nerve  cells  of  this  grey  reticular  formation  in  the  medulla  oblongata 
give  origin  to  fibres  which  bifurcate  and  pass  both  upwards,  probably 
serving  as  association  fibres  for  the  same  area  in  the  pons,  and 
downwards  towards  the  upper  part  of  the  cord.  Some  also  are  said 
to  give  origin  to  fibres,  which  either  after  traversing  the  raphe  or 
passing  directly  to  the  same  side  as  arched  fibres,  eventually  enter 
the  cerebellum  through  the  inferior  peduncle  (Van  Gehuchten). 

Ventro-laterally  is  the  olive,  within  which  is  developed  a  peculiar 
wavy  lamina  of  grey  matter  containing  a  large  number  of  nerve-cells ; 
this  is  the  dentate  nudeus  of  the  olive.  The  lamina  is  incomplete  at  its 
mesial  aspect  Onlus  olivce),  and  here  a  large  number  of  fibres  issue,  and, 
passing  through  the  raphe,  course  as  internal  arcuate  fibres  to  the 
opposite  restiform  body,  and  thus  to  the  cerebellum.     Some,  however. 


THK   MEDULLA   OBLONGATA.  381 

turn  sharply  round  and  course  helow  the  dentate  nucleus,  forming  an 
investment  and  capsule  to  it  (siliqiia  olivce),  and  pass  towards  the 
restiform  body  of  the  same  side :  but  the  main  connection  of  the 
olivary  nucleus  is  with  the  cerebellar  hemisphere  of  the  opposite  side. 
The  olives  receive  numerous  collaterals  from  the  neighbouring  white 
columns,  including  a  few  from  the  pyramids.  Just  dorsal,  or  dorso- 
lateral to  the  olive,  is  the  continuation  upwards  of  the  ventral  spino 
cerebelkvr  bundle  (tract  of  Gowers)  of  the  spinal  cord ;  the  continuation 
of  the  dorsal  spino-cerehellar  hundle  (tract  of  Flechsig),  just  above  it, 
is  now  passing  into  the  restiform  body. 

A  tract  of  fibres  which  arise  within  the  thalamus  passes  OA^er  the 
lateral  surface  of  the  nucleus  olivse  and  ends  within  its  grey  matter 
(thalamo-olmivij  trad,  central  tegmental  trad  of  Bechterew).  The  cells 
of  the  dentate  nucleus  have  numerous  dendrons ;  their  axons  all  pass 
towards  the  hilus,  where  they  emerge,  and,  for  the  most  part,  cross 
the  raphe,  pierce  the  opposite  olivary  nucleus  and  pass,  as  already 
mentioned,  into  the  restiform  body  (lAiro-cerehellar  trod). 

Nerves  arising  from  the  medulla  oblongata. — The  12th,  11th,  10th, 
9th,  and  8th  nerves  all  take  origin  in  the  medulla  oblongata,  and  their 
fibres  may  be  seen  emerging  on  either  side,  those  of  the  12th  ventrally 
between  the  pyramid  and  olive,  and  those  of  the  other  three  nerves  in 
succession  at  the  side  of  the  medulla  oblongata  between  the  olive  and 
restiform  body. 

The  Xllth  or  hypoglossal  nerve  arises  from  a  well-marked  nucleus 
of  large  cells,  similar  to  those  of  the  anterior  horn  of  the  cord.  This 
nucleus  is  situated  : — in  the  lower  part  of  the  bulb,  A'entro-lateral  to 
the  central  canal  (fig.  447) ;  in  the  upper  part,  near  to  the  floor  of  the 
4th  ventricle,  close  to  the  middle  line  (figs.  448,  449).  None  of  the 
fibres  cross  to  the  opposite  side ;  according  to  Van  Gehuchten,  this  is 
true  of  all  the  cranial  nerves,  except  a  iew  fibres  of  the  .3rd  nerve  and 
the  whole  of  the  4th  nerve.  The  hypoglossal  nucleus  extends  through- 
out about  the  lower  two-thirds  of  the  bulb  (fig.  450,  nXII.).  It 
receives  many  collaterals  from  adjacent  sensory  tracts  in  the  reticular 
formation  and  from  the  descending  sensory  nuclei  of  the  5th,  9th,  and 
10th  nerves,  as  well  as  from  the  posterior  longitudinal  bundle.  These 
form  a  plexus  of  fine  fibrils  within  the  nucleus  which  is  highly 
■characteristic.     A  similar  plexus  is  seen  in  the  oculomotor  nucleus. 

AJesial  to  the  hypoglossal  nucleus,  in  the  open  part  of  the  medulla 
oblongata,  is  the  nudeus  of  the  fasdculns  teres,  a  column  of  moderate 
sized  cells  which  extends  towards  the  caudal  end  of  the  pons  and 
appears  to  receive  fibres  from  the  cerebellum  (Edinger). 

The  Xlth  nerve  or  spinal  accessory  begins  to  take  origin  from  cells 


382 


THE   ESSENTIALS   OF   HISTOLOGY. 


in  the  lateral  part  of  the  grey  matter  of  the  spinal  cord  as  low  dowrt 
as  the  5th  cervical  nerve.  Its  fibres  from  the  cord  (spinal  fibres)  are 
those  to  the  (voluntary)  sternomastoid  and  trapezius  muscles.  They 
pass  from  the  cells  of  origin  in  the  lateral  horn  {motor  nucleus)  at  first 
dorsalwards  and  then  take  a  sharp  bend  outwards  through  the  lateral 


Fig.  450.— DiAciRAM.s  illustrating  theorigin  and  relations  of  the  root- 
fibres  OF  THE  CRANIAL  NERVES. 

A.  Efferent  fibres  only  :  profile  view. 

B.  Shows  on  the  left  the  motor  nuclei  and  efferent  fibres,  except  those  of  the  4th  nerve, 

and  on  the  right  side  the  afferent  fibres  :  surface  view. 


column  to  emerge  at  the  side  of  the  cord  and  medulla  oblongata.  The 
bulbar  fibres  (which  join  the  vagus)  take  origin  in  a  nucleus  of 
relatively  small  cells  which  lies  dorso-laterally  to  the  central  canal  of 
the  medulla  oblongata  and  behind  the  hypoglossal  nucleus.  This 
nucleus  is  continuous  above  with  the  corresponding  nucleus  of  the 
vagus,  and  with  it  forms  the  doisal  accessm-y-vagus  nucleus  (figs.  447  to- 
450).  Below,  it  extends  nearly  as  far  as  the  first  cervical  nerve ;: 
its  upper  part  (vagal  part)  is  in  the  floor  of  the  4th  ventricle  lateral  ta 


THE   MEDULLA   OBLONGATA. 


383 


the  hypoglossal  nucleus,  ami  oxtcnds  nearly  as  far  as  the  lower 
bordei'  of  the  pons.  Of  the  whole  nucleus  about  the  lower  two-thirds, 
i.r.  as  fai-  as  the  lower  end  of  the  calamus  scriptorius  gives  origin  to 
fibres  of  the  accessory.  These  fibres,  as  already  stated,  join  the  vagus, 
to  which  they  supply  the  motor  fibres  of  the  thyroarytenoid  muscles 
(Van  Gehuchten).     The  12th  and  11th  nerves  are  entirely  eti'erent. 


a'.^.JT  yir/ 


Fig.  451. — Plan  of  the  origin  op  the  XIIth  and  Xth  nerves. 

pyr,  pyramid  ;  n.XII.,  nucleus  of  hypoglossal ;  XJI.,  hypoglossal  nerve ;  d.n.X.  Jf  A.,  dorsal 
nucleus  of  vagus  and  accessory  ;  n.<i-iub.,  nucleus  ambiguus  ;  /.«.,  fasciculus  solitarius 
(descending  root  of  vagus  and  glosso-pharyngeal) ;  f.s.n.,  its  nucleus;  A'.,  crossing 
motor  fibre  of  vagus  ;  g,  cell  in  ganglion  of  vagus  giving  origin  to  a  sensory  fibre  ; 
il.  v.,  descending  root  of  fifth  ;  c.r.,  corpus  restiforme. 


The  Xth  nerve  or  vagus  (pneumogastric)  contains  both  motor 
(efferent)  and  sensory  (afferent)  fibres.  The  efferent  fibres  arise  (1)  from 
the  upper  part  of  the  dorsal  accessory-vagus  nucleus  just  described, 
(2)  from  a  nucleus  of  grey  matter  containing  large  cells  situated  in 
the  reticular  formation  (figs.  449,  451,  n.amh.).  This  nucleus  begins 
near  the  loM^er  limit  of  the  bulb  and  extends  nearly  to  the  facial 
nucleus,  which  it  resembles  in  general  position  :  it  is  known  as  the 
nvcleus  ambiguus  {ventral  nucleus  of  the  Xth  nerve).  The  axons  of  its 
cells  are  directed  at  first  backwards  and  inwards  and  then  turn  sharply 
round  in  the  lateral  direction  to  join  the  rest  of  the  issuing  fibres 
of  the  nerve,  coursing  in  the  same  manner  as  the  spinal  fibres  of 
the  accessory ;  indeed,  this  nucleus  is  continuous  below  with  the 
column  of  cells  from  which  those  fibres  take  origin. 

The  sensory  fibres  take  origin  in  the  ganglion  of  the  root  and  the 
ganglion  of  the  trunk  {jugular  and  plexiform  ganglia)  of  the  nerve,  from 


384  THE   ESSENTIALS  OF   HISTOLOGY. 

unipolar  cells  like  those  of  the  spinal  ganglia  (fig.  451,  g).  They  enter 
the  medulla  oblongata,  and  then  bifurcate,  one  branch,  a  short 
(ascending)  one,  passing  at  once  into  the  upper  sensory  or  principal 
nucleus,  the  other,  a  long  one,  descending.  The  descending  fibres 
(with  similar  fibres  of  the  IXth  and  those  of  the  pars  intermedia  of 
the  Vllth)  form  the  so-called  fasciculus  solitarius  (figs.  448,  449,  451) 
{descending  root  of  facial,  vagus,  and  glossopharyngeal),  which  is  traceable 
to  the  lower  limit  of  the  medulla  oblongata ;  they  end  in  grey  matter 
which  lies  along  its  mesial  border  (descending  nucleus  of  facial,  vagus, 
and  glossopharyngeal).  This  nucleus  approaches  the  middle  line  as  it 
descends,  and  in  some  animals  terminates  by  joining  its  fellow  of  the 
opposite  side  over  the  central  canal  to  form  the  commissural  nucleus  of 
Cajal.  The  upper  sensory  nucleus  [principal  nucleus),  in  which  the 
short  branches  from  the  sensory  root  end,  lies  in  grey  matter  near  the 
floor  of  the  ventricle,  and  is  continuous  with  that  which  accompanies 
the  fasciculus  solitarius. 

The  IXth  or  glossopharyngeal  nerve  also  contains  both  eff'erent  and 
afferent  fibres.  The  former  have  their  cells  of  origin  in  a  special 
nucleus  which  occupies  a  position  similar  to  that  of  the  nucleus 
ambiguus,  but  is  mesial  to  the  anterior  end  of  that  nucleus,  and  just 
below  the  nucleus  of  the  facial  {motor  nucleus  of  glossopharyngeal).  The 
afferent  fibres  of  the  nerve  arise  in  the  upper  or  jugular  and  petrosal 
ganglia  from  unipolar  cells  like  those  of  the  spinal  ganglia.  Their 
central  axons  enter  the  medulla  oblongata,  and,  like  other  sensory 
fibres,  bifurcate  into  two  branches,  ascending  and  descending.  Their 
course  is  like  those  of  the  vagus,  the  descending  passing  down  in  the 
fasciculus  solitarius  (extending  to  about  one-third  of  its  length,  Bruce), 
and  ending  by  arborising  in  the  grey  matter  accompanying  it  (descend- 
ing root  and  nucleus),  while  the  ascending  branches  pass  nearly 
horizontally  backwards  and  inwards  to  a  nucleus  (principal  nucleus) 
beneath  the  inferior  fovea  of  the  floor  of  the  ventricle  which  is  con- 
tinuous with  the  upper  end  of  the  nucleus  of  the  descending  root.  The 
arrangement  is  almost  exactly  a  counterpart  of  that  of  the  vagus 
shown  in  the  diagram  given  in  fig.  451. 

According  to  Edinger  the  sensory  nuclei  of  these  nerves  receive  fibres  from 
the  cerebellum,  constituting  a  cerebello-bulhar  tract,  whicli  is  much  better 
marked  in  lower  vertebrata  than  in  man  and  mammals. 

The  Vlllth  nerve. — A  section  taken  through  the  uppermost  jxirt  of  the 
olivary  prominence  will  still  show  very  much  the  same  form  and 
structural  arrangements  as  that  just  described.  The  nucleus  of  the 
hypoglossal  (fig.  452,  n.XII.)  is  still  visible  in  the  grey  matter  of  the 
floor  of  the  ventricle  near  the  middle  line,  but  the  nerve  which  is  now 


THE   MEDULI.A   OBLONGATA. 


385 


seen  connected  with  the  Literal  part  is  the  eighth  or  auditory  {VI II.), 
the  bundles  of  which,  as  they  enter  the  bulb,  embrace  the  inferior 
crus  of  the  cerebellum  {corpus  restiforme,  c.r.),  which  is  now  passing 
into  that  organ.  The  origin  of  the  eighth  nerve  is  thus  subdivided 
into  two  principal  parts,  known  respectively  as  the  dorsal  or  cochlear 
and  the  ventral  or  vestilndar  divisions  (fig.  452). 


nvm, 


njcn 


Fig.  452. — Transverse  section  of  the  upper  part  of  the  medulla 
OBLONGATA.     |.     (Schwalbe.) 

Pll,  pyramid  ;  o,  olivary  nucleus  ;  V,  descending  root  of  the  fifth  nerve  ;  VIII. ,  root  of 
the  auditory  nerve,  formed  of  two  parts,  o,  cochlear,  and  b,  vestibular,  which  inclose 
the  restiform  body,  c.r.;  n.VIIIp.,  principal  nucleus  of  the  vestibular  division; 
7).  Vlllac,  ventral  or  accessory  nucleus  of  the  cochlear  division  ;  </,  lateral  nucleus  of 
the  cochlear  division;  n.f.t.,  nucleus  of  the  funiculus  teres;  n.XII.,  nucleus  of  the 
hypoglossal ;  r,  raphe  ;  f.r.,  reticular  formation. 

The  real  origin  of  the  nerve  fibres  in  these  roots  is  in  the  ganglion 
of  the  cochlea  and  the  ganglion  of  Scarpa  respectively.  These  ganglia, 
which  are  situated  at  the  periphery  within  and  near  the  internal  ear, 
are  composed  of  bipolar  cells,  of  which  the  peripheral  axons  end  by 
ramifying  amongst  the  cells  of  the  auditory  epithelium,  and  the 
central  axons  form  the  cochlear  and  the  vestibular  divisions  of  the 
auditory  nerve  and  pass  into  the  medulla  oblongata  in  the  manner 
here  described. 

The  fibres  of  the  dorsal  or  coclilear  division  (cochlear  nerve) 
bifurcate  as  they  enter  the  medulla  oblongata.  Each  fibre  divides 
into  a  thick  and  a  thin  branch.  The  thicker  branches  pass  partly  to 
a  mass  of  ganglion  cells  which  is  wedged  in  between  the  two  roots 
and  the  restiform  body,  and  is  known  as  the  accessory  auditory  nucleus 

2b 


386 


THE   ESSENTIALS   OF  HISTOLOGY. 


(figs.  452  ;  453,  n.acc),  applying  themselves  with  a  peculiar  form  of 
terminal  arborisation  to  the  cells  of  this  nucleus,  partly  over  the 
restiform  body  to  terminate  in  a  prominent  mass  of  grey  matter  which 
overlies  that  body  and  also  extends  to  the  lateral  part  of  the  floor  of  the 
fourth  ventricle  at  its  widest  part  {lateral  nucleus,  tuberculum  acusticum). 
The  cells  of  the  tubercle  have  a  peculiar  spindle  shape  and  are  set 
vertically  to  the  surface.  They  appear  to  begin  in  the  root  itself,  lying 
amongst  the  fibres  of  the  nerve.     Here  they  are  sometimes  spoken  of 


FIBRES  TO  NUCL.LEMNISCI 
ftCORPORA  QUADRIGEMINA 


NERVE-ENDINGS 

in  organ  of  corti 

Fig.  453. — Plan  of  the  course  and  connections  ov  the  fibres  forming 
the  cochlear  root  of  the  auditory  nerve. 

r.,  restifomi  body;  V.,  desoendintr  root  of  the  fifth  nerve;  tub.a.c,  tuberculum  acusticum; 
n.acc,  accessory  nucleus;  s.o.,  superior  olive;  n.tr.,  nucleus  of  trapezium;  n.VI., 
nucleus  of  sixth  nerve  ;   VI.,  issuing  root  fibre  of  sixtli  nerve. 

as  forming  the  "ganglion  of  the  root."  The  thinner  branches  of  the 
bifurcated  cochlear  fibres  pass  downwards  for  a  certain  distance  and 
break  up  into  a  plexus  of  fine  fibrils. 

These  two  nuclei,  viz.,  the  accessory  nucleus  and  the  acoustic 
tubercle,  are  the  nuclei  of  ending  of  the  cochlear  fibres.  From  their 
nerve-cells  new  fibres  arise  which  continue  the  auditory  path  centrally 
(see  fig.  45-3).  Those  from  the  accessory  nucleus  enter  the  trapezium 
— which  consists  of  transverse  fibres  running  behind  the  pyramid 
bundles  of  the  pons  Varolii — and  pass  in  it  partly  to  the  superior 
olive  and  trapezoid  nucleus  of  the  same  side  of  the  pons,  but  mostly 
to  the  corresponding  structures  on  the  opposite  side.  Some  end  in 
those  nuclei,  but  others  merely  traverse  them,  giving  off"  numerous 
collaterals  to  them  and  to  the  superior  olives  and  other  nuclei  close 
by  (see  p.  392),  and  then  turn  upwards  in  the  lateral  part  of  the 
tract  of  the    fillet   to   pass  ultimately  towards   the   inferior  corpora 


THE   MEDULLA   OBLONGATA.  387 

(|iuulngomina ;  in  tending  towards  these  structures  at  the  side  of  the 
mid-brain  they  form  the  lateral  fillet,  or  fillet  of  lieil,  which  is  there 
conspicuous.  Some  of  the  fibres  from  the  cells  of  the  accessory 
nucleus  do  not  pass  directly  to  the  trapezium,  but  first  curve  round 
the  restiform  body  (Held);  these  form  the  most  dorsally  situated  fibres 
of  the  trapezium.  The  fibres  which  arise  in  the  acoustic  tubercle  pass 
for  the  most  part  over  the  fioor  of  the  fourth  ventricle,  where  they 
are  seen  superficially  as  the  medullary  or  acoustic  strice,  and,  entering 
the  raphe,  traverse  it  from  behind  forwards,  and  then  join  the  others 
from  the  accessory  nucleus  in  their  course  to  the  superior  olive  and 
lateral  fillet  of  which  they  constitute  the  deeper  layer.  A  few  fibres 
are  directed  into  the  fillet  of  the  same  side  as  their  cells  of  origin. 

Edinger  states  that,  at  least  in  the  dog,  all  the  fibres  of  the 
trapezium  end  in  its  nucleus  or  in  the  superior  olivary  nucleus,  the 
central  acoustic  path  being  wholly  continued,  so  far  as  the  trapezium 
fibres  are  concerned,  by  fresh  neurones,  the  cell-bodies  of  which  lie  in 
those  nuclei,  and  the  axons  of  which  pass  into  the  lateral  fillet.  On 
the  other  hand,  from  the  cells  in  the  tuberculum  acusticum,  the  axons 
are  said  to  be  continued  upwards  in  the  opposite  lateral  fillet  without 
the  intervention  of  any  corresponding  nuclei.  The  lateral  fillet  passes 
above  into  the  posterior  colliculus  of  the  mid-brain. 

The  accessory  nucleus  also  receives  fibres  from  the  trapezium,  which 
end  by  ramifying  amongst  its  cells.  These  are  perhaps  derived  from 
the  accessory  nucleus  of  the  opposite  side. 

Both  sets  of  fibres  (from  the  accessory  nucleus  and  tuberculum) 
give  off  collaterals  near  their  origin,  which  terminate  within  these 
nuclei. 

The  ventral  or  vestibular  division  (vestibular  nerve),  which  enters 
a  little  in  front  of  (above)  the  cochlear  division,  passes  between  the 
restiform  body  and  the  descending  root  of  the  fifth  (fig.  452),  to  enter 
a  mass  of  grey  matter  containing  for  the  most  part  cells  of  small  size, 
which  is  termed  the  principal  w  dorsal  nucleus  of  the  vestibular 
division.  Here  each  of  its  fibres  divides  with  a  Y-shaped  division 
into  an  a.scending  and  a  descending  branch  (fig.  454).  The  descending 
branches  are  collected  into  small  bundles  {descending  vestibular  root) 
which  run  downwards  towards  the  lower  part  of  the  medulla  oblongata, 
and  gradually  end  by  arborising  around  cells  in  the  adjacent  grey 
matter  {descending  vestibular  nucleus),  which  is  continued  down  from  the 
principal  nucleus.  The  ascending  branches  pass  upwards  on  the  inner 
side  of  the  restiform  body  towards  the  nucleus  tecti  of  the  cerebellum. 
In  their  course  they  give  oft'  numerous  collaterals  which  arborise  round 
the  large  cells  of  two  nuclei  which  occur  in  this  part  of  the  medulla 


388 


THE   ESSENTIALS  OF   HISTOLOGY. 


oblongata  and  pons  near  the  outer  part  of  the  floor  of  the  fourth 

ventricle.     These  two  nuclei  are  termed  the  nvdeus  of  Deiters  and  the 

nucleus  of  Bechterew  respectively  (fig.  454). 

Van  Gehuchten  states  that  the  nucleus  of  Bechterew  aloue  recei%'es  fibres 
from  the  ascending  branches  and  that  all  the  other  nuclei  (dorsal,  descending, 
and  nucleus  of  Deiters)  are  furnished  with  fibres  from  the  descending 
branches. 


TO  VERMIS 


FIBRES    O 

VESTIBULA 

ROOT 


NERVE 
ENDINGS 
IN  MACUL/E 
&  AMPULL/E 


Fig.  454. — Plan  of  the  course  and  coxxections  of  the  fibkes  forming 

the  vestibular  root  of  the  auditory  nerve. 
r.,  restiform  body;  V.,  descending  root  of  fifth  nerve;  p.,  cells  of  principal  nucleus  of 
vestibular  root ;  d,  fibres  of  descending  vestibular  root ;  n.d.,  a  cell  of  the  descending 
vestibular  nucleus  ;  D.,  cells  of  nucleus  of  Deiters  ;  B,  cells  of  nucleus  of  Bechterew  ; 
n.t.,  cells  of  nucleus  tecti  (fastigii)  of  the  cerebellum  ;  p.l.b.,  fibres  of  posterior  longi- 
tudinal bundle.  Xo  attempt  lias  been  made  in  this  diagram  to  represent  the  actual 
positions  of  the  several  nuclei.  Thus  a  large  part  of  Deiters'  nucleus  lies  dorsal  to  and 
in  the  immediate  vicinity  of  the  restiform  body. 

The  nucleus  of  Deiters  is  especially  characterised  by  the  large  size 
of  its  cells  and  by  the  manner  in  which  they  are  enveloped  as  by  a 
basket-work  by  the  ramifications  of  the  collaterals  in  question.  From 
these  cells  fibres  arise  which  pass  to  the  posterior  longitudinal  bundles 
of  both  sides :  in  these  the  fibres  bifurcate  (Cajal),  one  branch  passing 
upwards  to  the  oculomotor  nucleus  and  giving  off  collaterals  to  the 
nucleus  of  the  sixth  nerve,  and  the  other  downwards,  eventually 
reaching  the  anterior  column  of  the  spinal  cord  (antero-lateral 
descending  tract)  and  terminating  by  arborisations  amongst  the  cells  of 
the  anterior  horn  (see  p.  365).  By  means  of  the  collateral  fibres  which 
supply  the  sixth  and  oculomotor  nuclei  it  is  probable  that  the  conjugate 
movements  of  the  two  eyes  are  brought  about.  Fibres  have  also  been 
described  as  passing  from  Deiters'  nucleus  to  the  nucleus  tecti  of  the 


THE    MEDULLA   OBLONGATA.  389 

cerebellum.  Owing  to  its  connections  with  the  semicircular  canals, 
the  cerebellum,  the  oculomotor  nuclei,  and  the  nuclei  in  the  anterior 
horn  of  the  spinal  cord,  this  nucleus  has  important  functions  in 
connection  with  co-ordination  of  head  and  eye  movements  and 
equilibration  in  general. 

The  fil)res  which  originate  in  the  nucleus  of  Bechterew  pass  into 
the  reticular  formation  and  become  longitudinal,  but  their  destination 
is  not  certainly  known.  Some  are  said  to  pass  into  the  anterior 
column  of  the  cord. 

The  reticular  formation  still  occupies  the  .greater  part  of  each  lateral 
half  of  the  bulb  between  the  grey  matter  at  the  floor  of  the  fourth 
ventricle  and  the  pyramids,  and  a  small  portion  of  the  olivary  nucleus 
may  still  be  seen,  as  may  also  the  descending  root  of  the  fifth  nerve 
with  its  adjacent  grey  matter. 

The  restiform  body  is  formed  partly  of  the  fibres  of  the  cerebellar 
tract  of  Flechsig  of  the  same  side,  which  are  derived  below  from  the 
cells  of  Clarke's  column,  and  pass  above  into  the  middle  lobe  of  the 
cereV)ellum,  partly  of  fibres  from  the  opposite  olivary  nucleus,  and 
partly  of  fibres  from  the  olivary  nucleus  of  the  same  side.  The  olivary 
fibres  pass  mainly  to  the  cerebellar  hemisphere.  According  to  some 
authorities  the  restiform  body  contains  fibres  derived  from  the 
nucleus  gracilis  and  nucleus  cuneatus  of  the  opposite  side.  It 
is  said  also  to  receive  some  fibres  from  a  nucleus  which  lies  just 
outside  the  main  mass  of  grey  matter  of  the  funiculus  cuneatus,  and 
is  known  as  the  outer  cuneate  nucleus. 

The  floor  of  the  fourth  ventricle  is  covered  by  a  layer  of  ciliated 
epithelium-cells,  continuous  below  with  those  lining  the  central  canal,, 
and  above,  through  the  Sylvian  aqueduct,  with  the  epithelium  of  the 
third  and  lateral  ventricles.  The  epithelium  rests  upon,  and  the  pro- 
longed extremities  of  its  cells  assist  in  forming,  a  layer  of  tissue 
known  as  the  ependyma  of  the  ventricle.  The  fourth  ventricle  is  roofed 
over  by  a  layer  of  pia-mater,  with  projecting  choroid  plexuses,  the 
under  surface  of  which  is  covered  by  a  thin  epithelial  layer  continuous 
at  each  side  with  the  ciliated  epithelium  of  the  floor.  The  roof  becomes 
somewhat  thickened  as  it  is  continued  into  the  ependymal  layer  of  the 
floor  of  the  ventricle ;  this  thickened  part  (tcenia  or  ligula,  figs.  448, 
449,  t),  is  often  left  attached  when  the  thin  epithelial  roof  is  removed 
along  with  the  pia-mater  which  covers  it. 


390  THE   ESSENTIALS   OF   HISTOLOGY 


LESSONS  XLIT.   and  XLIII. 

THE  PONS    VAROLII,  MESENCF.PHALON,   AND 
TEA  LA  MENCEPHALON. 

\.  Sections  through  the  lower,  middle,  and  upper  parts  of  the  pons  Varolii. 

2.  Sections  across  the  region  of  the  corpora  quadrigemina,  one  at  the  level 
of  the  inferior,  the  other  at  the  level  of  the  superior,  pair. 

3.  A  section  across  the  posterior  part  of  the  third  ventricle  passing  through 
the  optic  thalami. 

In  all  the  above  sections  sketch  under  a  low  power  the  general  arrange- 
ment of  the  grey  and  white  matter,  inserting  the  positions  of  the  chief  group.s 
of  nerve-cells. 

[The  tissue  is  hardened  and  the  sections  are  prepared,  stained,  aud  mounted 
in  the  same  way  as  the  spinal  cord  and  medulla  oblongata.] 


THE    PONS    VAROLII. 

Sections  through  the  lower  part  of  the  pons  (figs.  455,  457,  459) 
show  much  the  same  arrangement  of  grey  and  white  matter  as  that 
met  with  at  the  upper  part  of  the  medulla  ol)longata,  but  the  general 
appearance  of  the  sections  is  much  modified  by  the  presence  of  a  large 
mimber  of  transversely  coursing  bundles  of  nerve-fibres,  most  if  not  all 
of  which  are  passing  to  the  hemispheres  of  the  cerebellum  (fibres  of 
middle  peduncle  of  cerebellum). ^  Intermingled  with  these  bundles  is 
a  considerable  amount  of  grey  matter  {nuclei  pontis)  from  the  cells  of 
which  the  fibres  of  the  middle  peduncle  (of  the  opposite  side)  are 
derived.^  Amongst  the  cells  of  the  nuclei  pontis  many  fibres  and 
collaterals  of  the  pyramidal  tract'  end,  and  the  cortico-pontine  fibres 
also  terminate  here  ;  thus  forming  a  connection  between  the  cerebral 
hemisphere  of  the  one  side  and  the  opposite  cerebellar  hemisphere 
(fig.  479).  The  continuation  of  the  pyramids  of  the  medulla  oblongata 
(fig.  455,  py)  is  embedded  between  these  transverse  bundles,  but  the 
pyramid  bundles  of  the  pons  are  much  larger  than  the  pyramids  of  the 
medulla  oblongata,  and,   in  addition  to  fibres  of  the  pyramidal  tract 

'  Some  of  the  most  anterior  of  these  peduncular  fibres  often  form  a  detached 
bundle  which  is  known  as  the  taenia  pontia  (fig.  461). 

-Other  of  these  fibres  have  been  described  as  arising  in  the  cerebellar  hemi- 
sphere and  crossing  the  raphe ;  some  becoming  lost  amongst  the  cells  of  the 
opposite  nucleus  pontis,  and  some  passing  to  the  reticular  formation,  there 
becoming  longitudinal.  But  tliis  double  origin  is  denied  by  Van  Gehuchten, 
apparently  with  good  reason. 


THE    PONS   VAROLII. 


391 


proper  {corticospinal  system),  derived  from  the  motor  area  of' the  cortex, 
they  are  largely  composed  (especially  the  postero-lateral  bundles)  of 
fibres  (cortico pontine  si/.'tfcni)  connecting  other  regions  of  the  cortex  with 
this  part  of  the  hind-brain.  The  pyramid  bundles  are  separated  from 
the  reticular  formation  by  deeper  transverse  fibres,  which  belong  to 


K/l/ 


-^ 


J^ 


Fig.  455.— Tkax.sver.se  .section  throi  gh  the  lo\\ermosi  part  ot  ihe  pons 
VAROLII.     |.     (From  a  pliotogiaph  ) 

V.I  v.,  fourth  ventricle;  c. ,  white  matter  of  cerebellar  hemisphere;  c.d.,  corpus  dentatum; 
fi.,  flocculus ;  c.r.,  corpus  restiforme ;  R,  bundle  of  Roller,  composed  of  the  descending 
branches  of  the  vestibular  uerve ;  D.  nucleus  of  Deiters ;  VIII.,  issuing  root  of  auditory 
nerve;  Fill.  J.,  principal  or  dorsal  nucleus  of  the  vestibular  nerve;  VIII. v.,  nucleus 
of  cochlear  portion  ;  ti:,  trapezium  ;  n.tr.,  its  nucleus  ;  /,  fillet ;  p. Lb.,  posterior  longi- 
tudinal bundle;  /.<■.,  formatio  reticularis;  n,  n',  n",  various  nuclei  within  it;  V.o.., 
de.scendiug  root  of  fifth  nerve;  s.g.,  sulDstantia  gelatinosa ;  s.o..  superior  olive; 
VII.,  issuing  root  of  facial  nerve;  n.VII.,  its  nucleus;  VI.,  root -bundles  of  sixth 
nerve  ;  -py,  pyramid  bundles  ;  n.p.,  nuclei  pontis. 

a  different  system  from  those  of  the  middle  peduncle.     They   form 

what  has  already  been  referred  to  as  the  frape:iuin  (figs.  453,  455) ;  a 

collection  of  fibres  which  forms  part  of  the  central  auditory  path,  and 

some  of  which  appear  to  1)e  commissural  between  the  auditory  nuclei 

of  the  two  sides.     The  fibres  of  the  trapezium  traverse  a  collection  of 

nerve-cells   which   lies    mesial    and    ventral   to   the    superior    olivary 

nucleus,  and  is  known  as  the  nucleus  of  the  trapezium  (fig.  453,  n.fr.). 

This  luii-leus  is  characterised  by  the  peculiar  chalice-like  synapses  which 
the  enteriucf  axons  of  the  larger  acoustic  fibres  form  with  the  ceil- bodies 


392  THE   ESSENTIALS   OF   HISTOLOGY. 

(Held)  (see  fig.  171,  p.  144).  According  to  Cajal  these  large  fibres  are  con- 
tinued directly  from  the  root-fibres  of  the  cochlear  nerve  and  are  not  derived 
from  the  cells  of  its  accessory  nucleus. 

The  olivary  nucleus  is  no  longer  seen,  but  there  are  one  or  two 
small  collections  of  grey  matter,  more  conspicuous  in  some  animals 
than  in  man,  which  lie  in  the  ventral  part  of  the  reticular  formation,  and 
are  known  as  the  superior  olivary  nucleus  (p.s.),  the  preolivary  nucleus,  and 
the  semilunar  nucleus  (Cajal).  All  these,  as  well  as  the  nucleus  of  the 
trapezium  itself,  are  connected  with  the  fibres  of  the  trapezium  which 
form  the  central  auditory  path,  some  of  these  fibres  either  ending  in 
the  nuclei  in  question  or  giving  off  to  them  numerous  collaterals ; 
whilst  from  the  cells  of  the  nuclei  axons  pass  into  the  trapezium  or 
into  the  adjacent  lateral  part  of  the  fillet  (see  p.  386).  On  the  other 
hand,  the  superior  olive  is  said  to  receive  fibres  from  the  posterior 
colliculi  of  the  corpora  quadrigemina.  The  nucleus  of  Deiters,  which 
begins  to  appear  in  the  upper  part  of  the  medulla  oblongata,  where  it 
has  been  already  studied  (p.  388),  extends  into  the  pons  Varolii,  where 
it  lies  near  the  floor  of  the  fourth  ventricle,  a  little  mesial  to  the  resti- 
form  body  {D,  fig.  455).  The  nerve-fibres  connected  with  its  cells  pass 
towards  the  middle  line  and  enter  the  posterior  longitudinal  bundle. 
Here,  as  already  stated,  they  divide,  one  branch  passing  upwards  in 
the  bundle  and  terminating  by  arborescence  chiefly  in  the  opposite 
oculomotor  nucleus  :  the  other  branch  extending  downwards  in  the 
medulla  oblongata  and  cord.  In  the  spinal  cord  they  are  found  in 
the  antero-lateral  descending  tract ;  fibres  from  each  nucleus  of  Deiters 
occur  in  both  of  these  tracts  (E.  H.  Fraser).  They  terminate  by 
arborescence  in  the  anterior  horn  of  the  spinal  cord. 

The  nerves  which  enter  or  emerge  from  the  grey  matter  of  this  region 
of  the  brain  are  part  of  the  eighth,  the  seventh,  the  sixth,  and  somewhat 
higher  up  the  fifth  cranial  nerves.  Of  these  the  eighth  (already 
considered)  and  fifth  are  connected  with  groups  of  nerve-cells  which 
occupy  the  grey  matter  opposite  the  external  border  of  the  floor  of 
the  ventricle ;  the  sixth  with  a  nucleus  which  is  also  placed  in  the 
grey  matter  of  the  floor  of  the  ventricle  but  nearer  the  middle  line, 
and  the  seventh  with  a  special  nucleus  which  lies  in  the  forniatio 
reticularis. 

The  Vllth  or  facial  nerve  and  the  nerve  of  Wrisberg  (pars 
intermedia). — The  motor  fibres  of  the  seventh  nerve  arise  from  the  facial 
nucleus  (in  the  formatio  reticularis)  which  is  homologous  with 
the  nucleus  ambiguus  seen  in  sections  of  the  medulla  oblongata.  It  has 
been  shown  that  the  motor  fibres  to  the  stapedius  arise  from  the  mesial 
part  of  the  nucleus  and  then  in  succession  those  of  the  external  ear 


THE   PONS   VAROLII. 


39a 


muscles,  those  of  the  mouth  and  tuoe,  and,  tinally,  from  a  group  of  cells 
situated  dorsally  to  the  rest,  the  motor  fibres  supplied  by  the  superior 
branch  of  the  nerve  (Marinesco,  Van  Gehuchten).  From  the  nucleus  of 
origin  the  fibres  first  pass  obliquely  backwards  to  the  Hoor  of  the 
ventricle,  then  longitudinally  upwards  for  a  short  distance  (figs.  450,  A, 
456),  and  finally  bend  oblicjuely  forwards  and  downwards  to  emerge 
between  the  transverse  fibres  at  the  side  of  the  pons.  None  of  its 
fibres  are  derived  from  the  micleus  of  the  sixth,  as  has  sometimes  been 
supposed.       As  it  curves  over  this  luicleus  it  gives  oft'  a  ])undle  of 


^//A 


//■'•" 


Fig.  4.56.— Plan  (transverse)  op  the  origin  of  the  sixth  and  seventh 

NERVES. 
VJ.,  sixth  nerve  ;  VII.,  seventh  nerve  ;  a.  VII.,  ascending  part  of  root  of  seventh  shown 
cut  across  near  the  floor  of  the  fourth  ventricle;  <j,  genu  of  seventh;  n.VI.,  chief 
nucleus  of  the  sixth  nerve;  n.VI.,  accessory  nucleus  of  sixth;  n.VIL,  nucleus 
of  seventh  ;  d.  V.,  descending  root  of  fifth  ;  pyr,  pyramid  bundles  ;  VIII.v.,  vestibular 
root  of  eighth  nerve. 

fine  fibres  which  cross  the  raphe,  but  their  destination  is  unknown.. 
The  nucleus  of  the  facial  receives  collaterals  from  the  adjacent  sensory 
tracts  in  the  formatio  reticularis. 

The  facial  is  not  a  purely  motor  nerve,  but  has  a  ganglion  upon  it  of 
the  spinal  type  {geniculate  ganglion)  from  which  fibres  arise  (fig.  450,  B} 
which  pass  centrally  into  the  pars  intermedia  of  Wrisberg,  which  enters 
the  pons  between  the  seventh  and  eighth  nerves,  and  the  fibres  of  which 
bifurcate  into  ascending  and  descending  branches  like  other  sensory 
nerves  ;  the  descending  branches  pass  into  the  solitary  bundle  and  end 
like  those  of  the  glossopharyngeal  in  the  upper  part  of  its  accompany- 
ing grey  matter.  The  peripheral  axons  of  the  cells  of  the  geniculate 
ganglion  pass  into  the  large  superficial  petrosal  and  chorda  tympani — 
to  which  they  probably  furnish  gustatory  fibres.     Other  (efferent)  fibres. 


394 


THE   ESSENTIALS   OF   HISTOLOGY. 


pass  into  the  pars  intermedia  and  ultimately  into  the  chorda  tympani 
from  certain  large  cells  which  occur  in  the  dorsal  part  of  the  facial 
nucleus.  These  are  probably  the  salivary  and  vasodilator  fibres  of  the 
chorda. 

The  Vlth  nerve  (abducens). — The  fibres  of  the  sixth  nerve  (figs.  450, 
456),  which  are  purely  motor,  pass  out  from  the  mesial  aspect  of  the 
nucleus   and  turn   forwards;    traversing   the   pyramid   bundles   they 


/sup.  cerebellar 
Dedu 


ace.  motor  root  of  Vth 
motor  nucl.  of  Vth 

sensory  nucl.  of  Vth 
sen.  root  fibres  of  Vth  —i. 
nucl.  in  tegmentum 
grey  matter  lateral 
to  fill( 

■white  matter  of  cere 
bellar  hemisphere 


nucl.  fun.  ter. 


fibres  of  pen 


nuclei  pontis 


central  bundle 

of  Vth 

post.  long.  bund. 

ant.  long.  bund, 
rub. -spin,  tract 

central  nucleus 
fillet 


trapezium 

fibres  of  pons 
raphe 

pyramid  bundles 
nuclei  pontis 

fibres  of  pons 


Fig.  457. 


-Sectiox  .across  the  middle  of  the  poxs  varolii. 
about  4  diameters. 


Magnified 


emerge  at  the  lower  margin  of  the  pons.  A  few  fibres  are  derived  from 
a  small  ventral  nucleus  lying  near  the  nucleus  of  the  facial ;  these  run  at 
first  backwards  and  then  turn  forwards  to  join  the  others  (Van 
Gehuchten)  (fig.  456,  n'  VI.). 

The  Vth  or  trigeminal  nerve  emerges  at  the  side  of  the  pons  in  two 
roots,  a  smaller  motor  and  a  larger  sensory. 

The  motor  root  is  derived  partly  from  fibres  which  arise  in  the  upper 
part  of  the  pons  and  lower  part  of  the  mesencephalon  from  large 
spherical  unipolar  nerve-cells  lying  at  the  side  of  the  grey  matter 
bounding  the  Sylvian  aqueduct  {accessort/  or  superior  motor  nucleiis  of 


THE   PONS   VAROLII. 


395 


fifth,  fig.  450,  nVms  ;  fig.  458,  m'n.V.),  partly  from  the  motor  miclem 
propel'  (figs.  450,  nVm  ;  458,  mn.V.)  which  lies  in  the  grey  matter  at 
the  lateral  edge  of  the  fourth  ventricle  (fig.  457).  As  they  pass  the 
motor  nucleus  proper  the  fil)res  from  the  superior  or  accessory  nucleus 
give  off  into  it  a  large  number  of  collaterals  which  ramify  l)etween  and 
around  its  cells. 


Fig.  458. — Plan  of  the  origin  of  the  fibres  of  the  fifth  nerve. 
G,  Gasserian  ganglion;  a,  b,  c,  three  divisions  of  the  nerve;  rn'.n.V.,  superior  motor 
nucleus;  m.n.V.,  principal  motor  nucleus;  p.s.n.V.,  principal  sensory  nucleus; 
d.s.n.V.,  descending  sensory  nucleus;  d.s.V.,  descending  root;  cV.,  c'V.,  central 
sensory  tracts  composed  of  fibres  emanating  from  the  sensory  nuclei ;  r,  plane  of 
the  raphe. 

The  fibres  of  the  sensory  root  are  derived  from  the  cells  of  the 
Gasserian  ganglion  which  are  homologous  with  the  cells  of  the  spinal 
ganglia.  These  fibres  of  the  sensory  root  when  traced  into  the  pons 
are  found  to  bifurcate,  the  ascending  branches  ending  in  a  mass  of 
grey  matter  {principal  sensory  nucleus  of  the  fifth,  fig.  458,  p.s.n.V.) 
lying  just  lateral  to  the  motor  nucleus,  while  the  descending 
branches  trend  downwards  into  the  medulla  oblongata  where  they  form 
the  descending  or  spinal  root  of  the  fifth  (fig.  458,  d.s.V.);  some 
even  reach  the  upper  part  of  the  spinal  cord.  They  lie  immediately 
lateral  to  and  in  close  connection  with  the  substantia  gelatinosa  Kolandi 


396  THE   ESSENTIALS   OF   HISTOLOGY. 

which  forms  the  inferior  sensor//  nucleus  (d.s.n.V.),  and  which  is  con- 
tinued above  into  the  principal  nucleus.  The  substantia  gelatinosa 
which  forms  the  sensory  nucleus  of  the  fifth  contains  numerous 
nerve-cells,  both  small  and  large  ;  many  of  the  small  cells  are  grouped 
into  nest-like  clusters  (islands  of  Calleja).  The  axons  of  the  larger  cells 
pass  for  the  most  part  across  the  raphe  to  the  formatio  reticularis  of 
the  opposite  side  where  they  reinforce  the  ascending  fibres  of  the 
intermediate  fillet,  but  some  ascend  in  the  fillet  of  the  same  side,  and 
others  pass  to  a  special  ascending  bundle  of  fibres  on  the  opposite  side  of 
the  raphe  which  lies  nearer  the  floor  of  the  fourth  ventricle,  and  in  the 
tegmentum  of  the  mid-brain  lies  lateral  to  the  posterior  longitudinal 
bundle ;  hence  it  is  continued  upwards  into  the  thalamus.  Collaterals 
are  given  off"  from  these  ascending  fibres  to  the  adjoining  grey  matter, 
and  especially  to  the  nucleus  of  the  facial  nerve.  Branches  also  pass 
downwards  in  the  formatio  reticularis. 

Descending  tracts  in  the  pons  and  medulla  oblongata. — Besides  the 
fibres  of  the  pyramids,  which  are  much  more  numerous  in  the  pons 
than  in  the  medulla  oblongata,  and  which  send  numerous  collaterals 
into  the  grey  matter  of  the  nuclei  pontis,  there  ai^e  several  other 
descending  tracts  of  fibres  in  the  pons  and  medulla  ol)longata.  One  of 
these,  which  lies  mesial  to  the  fillet  (see  page  398)  consists  of  fibres 
(cortico-bulbar)  passing  from  the  motor  cortex  towards  the  nuclei  of  the 
facial  and  hypoglossal.  In  the  crusta  of  the  mid-brain  these  fibres  lie 
mesial  to  the  ordinary  pyramidal  fibres,  but  they  then  leave  the  latter 
and  pass  into  the  ventral  part  of  the  tegmentum  and  are  continued  down- 
wards in  the  formatio  reticularis  into  the  medulla  oblongata.  Another 
bundle,  consisting  of  both  ascending  and  descending  fibres  (vestibulo- 
inotor),  is  very  distinct,  just  ventral  to  the  grey  matter  of  the  floor  of 
the  fourth  ventricle,  near  the  middle  line  ;  this  is  the  dorsal  ov  posteriw 
longitudinal  bundle ;  as  already  noticed  (pp.  388,  392.  See  also  p.  402) 
it  connects  Deiters'  nucleus  with  the  oculomotor  nucleus,  the  nucleus  of 
the  sixth,  and  the  anterior  horn  cells  of  the  spinal  cord  ;  it  probably  also 
receives  fibres  from  the  axons  of  the  large  cells  of  the  formatio  reticularis. 

Other  descending  tracts  in  the  pons  which  are  not  so  distinctly 
marked  in  the  normal  condition,  but  which  can  be  traced  by  the 
methods  of  Waller  and  Flechsig  are:— 1.  Momdmv's  bundle;  2.  The 
anterior  longitudinal  bundle ;  3.  The  ponto-spinal  lateral  tract ;  4.  The 
vestibulospinal  tract ;  5.  The  central  tract  of  the  tegmentum. 

Monakoio's  bundle  or  the  rubrospinal  tract  has  already  been  seen  as 
the  prepyramidal  tract  of  the  spinal  cord  (p.  365.  See  also  p.  403). 
Its  fibres  arise  from  the  cells  of  the  red  nucleus  of  the  mid-brain  of  the 
opposite  side,  crossing  the  raphe  in  Forel's  decussation  (p.  403,  foot- 


THE   PONS   VAROLII.  397 

note).  In  the  uppei-  part  of  the  pons  it  is  dorsal  to  the  mesial  fillet, 
but  lower  down  luiis  in  the  lateral  part  of  the  tegmentum,  dorsal  to 
the  lateral  fillet. 

The  anterior  longitudinal  bundle  {tectospinal  tract)  consists  of  fibres 
which  arise  in  the  opposite  superior  quadrigeminal  body,  these  cross 
the  raphe  in  Meynert's  decussation  (p.  40.3),  and  run  down  ventral  to 
the  posterior  longitudinal  bundle,  giving  off  collaterals  to  the  oculo- 
motor nuclei  and  the  nuclei  of  the  fourth  and  sixth  nerves  as  they 
descend.  Its  fibres  eventually  mix  with  those  of  the  posterior 
longitudinal  ])undle,  and  i^ass  into  the  anterior  column  of  the  cord, 
joining  the  antero-lateral  descending  tract  (p.  3G3). 

The  ponfo-spinal  lateral  tract  is  formed  of  fibres  which  arise  from  the 
large  cells  of  the  reticular  formation,  and  run  down  within  the  lateral 
area  of  this  formation  in  the  pons  and  medulla  oblongata  to  reach  the 
part  of  the  lateral  column  of  the  cord  which  lies  between  the  grey 
matter  and  the  tracts  of  Monakow  and  Gowers.  It  is,  however,  mixed 
here  with  many  fibres  of  different  origin.  The  destination  of  its  fibres 
is  similar  to  those  of  the  posterior  and  anterior  longitudinal  bundles, 
viz. :  the  adjacent  grey  matter  of  the  anterior  horn. 

The  vestibulospinal  tract  is  composed  of  fibres  derived  from  the  cells 
of  the  nuclei  of  Deiters  and  Bechterew,  and  is  therefore  similar  in  its 
origin  to  the  fibres  of  the  posterior  longitudinal  bundle.  The  destina- 
tion is  in  part  also  similar,  for  the  fibres  pass  below  into  the  anterior 
root  zone  of  the  cord  and  end  in  the  grey  matter  of  the  anterior  horn, 
but  in  their  course  downwards  they  lie  in  the  lateral  part  of  the  medulla 
oblongata  mixed  up  with  those  of  Monakow's  tract  and  the  ponto-spinal 
tract,  as  well  as  with  the  ascending  fibres  of  Gowers'  tract. 

The  central  tract  of  the  tegmentum  (Bechterew)  runs  in  the  pons 
exactly  in  the  middle  of  the  reticular  formation  of  the  tegmentum,  but 
in  the  medulla  oblongata  it  lies  more  ventrally  near  the  olivary 
nucleus,  beyond  which  it  has  not  been  traced.  The  origin  of  its 
fibres  is  not  certainly  known,  but  appears  to  be  the  thalamus ;  their 
destination  is  the  olivary  body  of  the  same  side  (see  p.  381,  thalamo- 
olivary  tract). 

Ascending  tracts  in  the  pons  and  medulla  oblongata. — In  the 
ventral  part  of  the  reticular  formation  is  a  very  well-marked  tract  of 
fibres,  somewhat  flattened  (narrow  in  section)  from  above  down  in  the 
pons ;  this  is  the  tract  of  the  fillet.  Its  fibres  are  partly  derived  from 
cells  in  the  nuclei  of  the  opposite  fasciculus  gracilis  and  fasciculus 
€uneatus  of  the  medulla  oblongata  which  have  crossed  the  raphe  as 
internal  arcuate  fibres ;  partly  from  cells  in  the  nuclei  which  are 
connected  with  the  terminations  of  the  sensory  cranial  nerves. 


398  THE   ESSENTIALS   OF   HISTOLOGY. 

In  the  mid-brain  the  fillet  splits  up  into  two  distinct  bundles  of  fibres 
termed  respectively  the  lateral  or  lower  and  the  intermediate  or  upper  fillet. 
The  fibres  of  the  lower  fillet  are  seen  at  the  side  of  the  mesencephalon 
{fillet  of  Reil),  and  are  traceable  partly  to  the  grey  matter  of  the 
inferior  corpora  quadrigemina  (fig.  465),  partly  to  the  mesial  geniculate 
body,  in  both  of  which  they  terminate ;  they  are  derived  from  the 
sensory  nuclei  of  the  medulla  oblongata  and  pons  (mainly  from  the 
acoustic  nuclei).  Those  of  the  upper  fillet  go  to  the  thalamus  (fig. 
469) ;  they  are  chiefly  the  fibres  from  the  cells  of  the  opposite  posterior 
columns  of  the  medulla  oblongata. 

Besides  the  ascending  fibres  of  the  tract  of  the  fillet,  this  bundle 
includes  a  certain  number  which  degenerate  below  a  section  of  the  tract 
and  are  therefore  descending  (centrifugal) :  their  cells  of  origin  appear 
to  lie  in  the  thalamus  ;  the  fibres  themselves  are  situated  mesial  to  the 
true  fillet  of  which  they  were  formerly  considered  to  be  a  part  (being 
termed  "mesial"  fillet):  they  form  a  thalamo-hulhar  tract.  Mesial  to  the 
tract  just  mentioned  is  a  bundle,  also  consisting  of  descending  fibres, 
belonging  to  the  system  of  the  pyramidal  tract,  and  containing  fibres 
which  eventually  come  into  relation  with  certain  of  the  cranial  motor 
nuclei  (Hoche).  This  constitutes  the  cortico-bulbar  trad  (see  page  396). 
In  the  crusta  it  lies  dorso-lateral  to  the  other  pyramidal  tract  fibres. 

Many  of  the  fibres  which  continue  the  sensory  path  of  the  cranial 
nerves  upwards  lie  in  the  formatio  reticularis  (tegmentum),  somewhat 
dorsal  to  the  tract  of  the  fillet,  forming  a  homologous  but  not  clearly 
defined  tract,  which  runs  up  through  the  pons  and  mid-brain  to 
terminate  in  the  subthalamic  region  and  in  the  optic  thalamus  (central 
tract  of  the  sensory  cranial  nerves).  Another  ascending  tract  is  the  special 
bundle  of  fibres  from  the  sensory  nucleus  of  the  5th  to  the  thalamus 
previously  referred  to  (p.  396). 

At  the  upper  part  of  the  pons  (fig.  459)  the  fourth  ventricle  narrows 
considerably  towards  the  Sylvian  aqueduct,  and  above  and  on  either 
side  of  it  two  considerable  masses  of  longitudinal  white  fibres  make 
their  appearance.  These  are  the  superior  peduncles  of  the  cerebellum, 
and  they  tend,  as  they  pass  forwards,  gradually  to  approach  the 
middle  line ;  across  which  immediately  below  and  in  the  region  of 
the  posterior  colliculi  of  the  corpora  quadrigemina  they  pass, 
decussating  with  one  another,  to  enter  the  formatio  reticularis  of  the 
opposite  side. 

The  fibres  of  the  superior  cerebellar  peduncles  for  the  most  part  take 
origin  in  the  cerebellum,  emerging  from  its  dentate  nucleus,  from  the 
cells  of  which  they  are  derived.  They  cross  the  raphe  in  the  mid-brain 
and  terminate  in  the  red  nucleus  of  the  (opposite)  tegmentum  ;  but  some 


TITK    PONS   VAROLII. 


39£^ 


of  them  give  oft'  a  branch  within  the  peihincle  before  crossing,  and  these 
branches  are  described  by  Cajal  as  forming  a  deiicending  cerehellar  bundle 
which  passes  downwards  towards  the  medulla  oblongata  and  spinal 
cord  on  the  inner  side  of  the  descending  root  of  the  fifth,  and  gives  off 


.       J,  intercrossing  of 

issuing  bundle  fourth  nerves 

of  IVtli 


root  bundle  nf  IVth 
ace.  motor  root  of  \  I  ii     — ■-- 

sup.  cerebell.  ped 

part  of  lateral  fillet  '  gggf 
post.  long,  bundle 

ant.  long,  bundl 


lateral  fillet 

decuss.  of  superior 
peduncles 


intermediate  fillet 

substantia  nigra 
central  nucleus 


crusta  or  pes  \ 
pedunculi   V 


breaking  up  of  crusta  into 
pyramid  bundles 


Fig.  459.— Transverse  section  through  the  upper  part  of  the  pons. 


collaterals  to  the  motor  nucleus  of  the  fifth,  to  the  facial  nucleus, 
to  the  nucleus  ambiguus,  and  to  the  anterior  horn  of  the  spinal  cord 
(fig.  480).  There  is  also  in  the  superior  peduncle  a  bundle  of  fibres 
which  are  derived  from  cells  in  the  thalamus  and  which  pass  down- 
wards in  the  peduncle. 

The  antero-lateral  ascending  trad  of  the  spinal  cord  (p.  365)  is  con- 


400 


THE   ESSENTIALS   OF   HISTOLOGY. 


N  ^'/' ;.. 


^.<=z.^ 


Fig.  460. — DLiORAii  to  show  the  mode  of  passage  of  the  fibres  of  the 

DORSAL  AND  VENTRAL  SPINO-CEREBELLAR  TRACTS  RESPECTIVELT  INTO  THE 
CEREBELLAR  VERMIS.   (F.  W.  Mott.) 

p.c.q.,  posterior  corpora  quadrigemina ;  s.v.,  superior  vermis  of  cerebellum  ;  d.a.c,  dorsal 
ascending  cerebellar  tract ;  v.a.c,  ventral  ascending  cerebellar  tract. 


Fig.  461. — The  corpora  qcadrigemina  and  neighbouring  parts  of  the 
BRAIN.     (Edinger  f rem  G.  Retzius. ) 

Brack,  ant.  cerebelli,  the  superior  cerebellar  peduncles,  between  them  the  anterior  medul- 
lary velum  partly  covered  by  the  lingula ;  Tr.  spino-cereb.  ventr.,  tract  of  Gowers 
curving  round  the  peduncle;  lemniscus,  the  lateral  fillet;  JV.  trochl.,  4th  nerve; 
N.  v.,  5th  nerve. 


THE   PONS   VAROLII. 


401 


tinned  up  in  the  lateral  column  of  the  medulla  oblongata  dorso-lateral 
to  the  olive  and  through  the  ventral  part  of  the  pons  Varolii  lateral  to 
the  pyramid  bundles,  but  at  about  the  level  of  the  exit  of  the  fifth 
nerve  many  of  its  fibres  begin  to  pass  obliquely  towards  the  dorso- 
lateral part  of  the  pons  (fig.  460),  where  the  superior  cerebellar 
peduncle  is  emerging  from  the  cerebellar  hemisphere.  The  tract  in 
question  {anterior  or  ventral  spino-cerebellar  trad)  now  curves  over  the 
lateral  aspect  of  this  peduncle  (fig.  461,  tr.  spino-cereb.  venfr.),  and  then 
takes  a  sharp  backward  turn,  passing  over  its  dorsal  aspect  to  enter 
the  middle  lobe  of  the  cerebellum  in  the  superior  medullary  velum. 


THE    MIDBRAIN    OR    MESENCEPHALON. 

In  sections  across  the  mesencephalon  (figs.  463  to  466),  the  upward 
continuity  of  the  parts  which  have  already  been  described  in  the  lower 
nerve-centres  can  still  in  great  measure  be  traced. 


s.m.V 


^zr"  XT 


Fig.  462.— Section  throcgh  the  okigix  of  the  fourth  nekve.     (Scliwalbe.) 

A,  transverse  sectif)ii  at  the  place  of  emergence  of  the  nerve-fibres.  B,  oblique  section 
carried  along  the  course  of  the  bundles  from  the  nucleus  of  origin  to  the  place  of 
eniergeuce.  Aq,  Sylvian  aqueduct,  with  its  surrounding  grey  matter  ;  JV,  the  nerve- 
bundles  emerging;  JV,  decussation  of  the  nerves  of  the  two  sides;  /F",  a  bundle 
passing  by  the  side  of  the  aqueduct  to  emerge  a  little  lower  down  ;  n.IV,  nucleus  of 
the  fourth  nerve ;  /,  lateral  fillet ;  s.c.p.,  superior  cerebellar  peduncle;  s.iu.  r.,  superior 
motor  root  of  the  fifth  nerve  ;  pi,  posterior  longitudinal  bundle ;  r,  raphe. 


The  Sylvian  aqueduct  (fig.  464,  Sy),  with  its  lining  of  ciliated 
epithelium,  represents  the  central  canal  of  the  cord  and  the  fourth 
ventricle  of  the  medulla  oblongata.  In  the  grey  matter  Avhich  sur- 
rounds it  [central  grey  matter)  there  is  seen  in  all  sections  of  the  region 
a  group  (column)  of  large  nerve-cells  {oculomotor  nucleus)  lying  ventrally 
on  each  side  of  the  middle  line,  close  to  the  reticular  formation.  From 
the  lower  part  of  this  column  the  root-bundles  of  the  fourth  nerve  arise 
at  the  lower  part  of  the  mesencephalon  and  pass  obliquely  backwards 
and  downwards  around  the  central  grey  matter,  decussating  with 
those  of  the  opposite  side   to  emerge  just   above  the   pons  Varolii 

2c 


402 


THE   ESSENTIALS  OF  HISTOLOGY. 


(figs.  459,  462).  Higher  up,  in  the  x^egion  of  the  anterior  colliculi,  the 
bundles  of  the  third  nerve  spring  from  a  continuation  of  the  same 
nucleus  (fig.  465,  n.IIL),  and  these  pass  forwards  and  downwards  with 
a  curved  coui'se  through  the  reticular  formation,  to  emerge  at  the 
mesial  side  of  the  crusta.  According  to  Van  Gehuchten  some  of 
the  fibres  of  the  3rd  nerve  cross  the  middle  line  and  emerge  with 
the  nerve  of  the  opposite  side. 

Tegmentum. — The  reticular  formation  of  the  pons  is  continued  up 
into  the  mesencephalon  and  is  here  known  as  the  tegmentum.  It  is  com- 
posed as  before  of  longitudinal  and  transverse  or  arcuate  bundles  of  fibres 
with  much  grey  matter  intermingled.  The  transverse  fibres  include 
the  decussating  fibres  of  the  superior  peduncles  of  the  cerebellum  {s.c.p.)y 


Fig.  463. — Outline  of  two  sections  across  the  mesencephalon. 
Xatixral  size. 
A,  througli  the  middle  of  the  inferior  corpora  quadrigemina.  B,  through  the  region  of 
the  superior  corpoi-a  quadrigeuiiua.  cr,  crusta;  s.n.,  substantia  nigi-a ;  t,  teg- 
mentum ;  s,  Sj'lvian  aqueduct,  with  its  surrounding  grey  matter;  c.q.,  grey  matter 
of  the  corpora  quadrigemina;  l.g.,  lateral  gi-oove  ;  pj.,  posterior  longitudinal  bnndle  ; 
d.  v.,  superior  root  of  the  fifth  nerve  ;  s.c.p.,  superior  cerebellar  peduncle  ;  /,  lateral 
fillet;  ///.,  third  nerve;  n.IIL,  its  nucleus.  The  dotted  circle  in  B  indicates  the 
situation  of  the  tegmental  or  red  nucleus. 

which  are  derived  from  cells  in  the  dentate  nucleus  of  the  cerebel- 
lum, and  on  reaching  the  opposite  side  bifurcate.  Their  ascending 
branches  become  gradually  lost  amongst  a  number  of  nerve-cells  which 
collectively  constitute  what  is  known  as  the  red  nucleus  or  nucleus  of 
the  tegmentum,  whilst  the  descending  branches  turn  downwards  in  the 
reticular  formation  (Cajal)  (see  p.  399).  But  some  of  the  fibres  of  the 
superior  peduncle  go  on  past  the  red  nucleus  to  the  ventral  part  of 
the  thalamus.  The  red  nucleus  also  receives  fibres  in  its  lateral  aspect 
which  are  derived  from  the  lenticular  nucleus  of  the  corpus  striatum, 
and  some  of  which  are  said  to  come  from  the  cerebral  cortex ;  these 
fibres  form  a  sort  of  capsule  to  the  red  nucleus  before  entering  it. 

Tracts  in  the  tegmentum. — L  Vestihulo-motor  tract;  posterior  longi- 
tudinal bundle. — This  is  well  marked  in  the  mid-brain,  and  gives  off 
many  collaterals  and  terminal  filires  to  the  oculomotor  nucleus  which 
is  immediately  dorsal  to  it.  The  bundle  largely  consists  of  nerve 
fibres  derived  from  the  cells  of  Deiters'  nucleus  (see  p.  388),  which 


THK   MESENCEPHALON.  403 

on  reaching  the  situation  of  the  bundle  either  on  the  same  or  on  the 
opposite  side,  bifurcate,  one  branch  ascending,  the  other  descending. 
But  it  receives  fibres  from  other  sources  than  Deiters'  nucleus,  e.g. 
from  large  cells  of  the  sensory  nucleus  of  the  oth,  and  from  large  cells 
in  the  reticular  formation  of  the  medulla  oblongata,  pons,  and  mid- 
brain. All  these  fibres,  like  those  from  Deiters'  nucleus,  bifurcate  on 
joining  the  bundle,  one  branch  passing  upwards,  the  other  downwards. 
Some  fibres  of  the  bundle  are  of  different  origin  from  the  rest,  arising 
beyond  the  oculomotor  nucleus.  These  are  very  fine ;  they  are 
descending  filjres,  and  are  traceable  from  the  cells  of  the  nucleus  of 
the  posterior  longitudiruil  bundle,  which  lies  in  front  of  the  Sylvian 
aqueduct  in  the  grey  matter  at  the  side  of  the  third  ventricle. 

Some  of  the  fibres  of  the  posterior  longitudinal  bundle  are  stated  to 
be  traceable  as  far  up  as  the  thalamus. 

The  bundle  gives  collaterals  not  only  to  the  oculomotor  nucleus  but 
also  to  the  nucleus  of  the  sixth,  and  probably  others  to  the  nuclei  of 
other  cranial  motor  nerves.  Its  descending  fibres  are  eventually 
continued  down  the  spinal  cord  in  the  antero-lateral  descending  tract, 
and  give  off  terminals  and  collaterals  to  the  anterior  horn. 

2.  Rubrospinal  trad ;  Monakow's  bundle. — The  cells  of  the  red  nucleus 
send  their  axons  downwards  and  forwards.  They  form  Monakow's 
bundle  or  the  rubrospinal  tract,  which  is  continued  below  into  the  pre- 
pyramidal  tract  of  the  spinal  cord. 

3.  Tectospinal  trad;  anterior  longitudinal  bundle. — Other  longitudinal 
fibres  of  the  tegmentum  are  those  of  the  fasciculus  retroflexus  of  Meynert 
lying  mesially  to  the  red  nucleus  and  passing  obliquely  downwards 
and  inwards  from  the  ganglion  of  the  habenula  to  the  interpeduncular 
ganglion  of  the  opposite  side,  and  the  bundle  of  Munzer,  which  passes  from 
the  posterior  tubercle  downwards  into  the  lateral  part  of  the  reticular 
formation  of  the  pons.  But  the  longest  and  most  important  is  the 
anterior  or  ventral  longitudinal  bundle,  which  passes  lateral  to  the  red 
nucleus  and  partly  through  it.  Although  the  red  nucleus  receives 
many  collaterals  from  this  bundle  the  fibres  of  the  bundle  are  derived, 
according  to  Held  and  Cajal,  from  cells  in  the  grey  matter  of  the 
opposite  anterior  tubercle  of  the  corpora  quadrigemina ;  these  cells 
send  their  axons  sweeping  round  the  central  grey  matter  just  central 
to  the  posterior  longitudinal  bundle  to  cross  in  the  raphe,  where  they 
form  the  fountain-like  decussation  of  Meynert  (fig.  464,  d').''-     The  down- 

^This  is  not  to  be  confounded  with  the  fountain-like  decussation  of  Forel 
(fig.  464,  d),  which  lies  nearer  the  ventral  part  of  the  tegmentum,  and  is  partly 
formed  by  the  intercrossing  of  Monakow's  bundle  and  partly  by  v.  Gudden's 
bundle  coming  from  the  corpora  mammillaria  to  end  in  the  tegmentum. 


404 


THE   ESSENTIALS   OF   HISTOLOGY. 


ward  continuation  of  the  tecto-spinal  tract  has  already  been  studied 
(pp.  397  and  365),  but  it  should  be  stated  that  the  prolongation  of  its 
fibres  into  the  anterior  column  of  the  spinal  cord  is  denied  by  Van 
(xehuchten,  who  traces  them  only  as  far  as  the  medulla  oblongata. 


Pig.  464. — Section  across  the  midbrain  through  the  inferior  pair  of 
CORPORA  QUADRIGEMINA.  Magnified  about  '.ih  diameters.  (From  a  photo- 
graph.) 

5»/.,  aqueduct  of  Sj'lvius ;  c.gr.,  central  grey  matter  of  the  aqueduct;  n  III. IV.,  group 
of  colls  forming  part  of  the  conjoined  nucleus  of  the  third  and  fourth  nerves  ;  c.q.p., 
one  of  the  posterior  corpora  quadrigehiina ;  f/r,  median  groove  separating  it  from 
that  of  the  opposite  side;  str.L,  stratum  lemnlsci  (layer  of  the  fillet),  forming  its 
superficial  laj'er  ; /',  upper  fillet  ;  ./",  lateral  fillet;  V.,  accessory  tnotor  root  of  fifth 
nerve;  p. Lb.,  posterior  longitudinal  bundle;  f.r.t.,  formatio  reticularis  tegmenti ; 
d,  d',  decussating  fibres  of  tegmenta  (fountain-decussations  of  Forcl  and  Meynert) ; 
s.c.p.,  superior  cei-ebellar  peduncles,  decussating;  p.p.,  pes  pedunculi  (crusta) ;  s.n., 
substantia  nigra;  g.i-p.,  interpeduncular  ganglion. 

4r.  Trad  of  the  fillet. — The  continuation  upwards  of  the  fillet  is  also 
apparent  in  this  part  of  the  brain.  Some  of  its  fibres  are  seen  passing 
in  an  oblique  manner  to  the  side  of  the  mesencephalon,  to  enter  the 
grey  matter  of  the  prominences  of  the  posterior  corpora  quadrigemina. 

This  part  is  the  lateral  fillet  (see  p.  398),  which  is  formed  chiefly  by 
fibres  derived  from  the  accessory  auditory,  the  inferior  olivary,  and  the 
trapezoid  nuclei  of  the  opposite  side,  forming  the  central  acoustic  tract. 


THE   MESENCEPHALON.  405 

Its  fibres  send  minioious  collaterals  to  the  i)osterior  tubercle  (fig.  46')) 
and  a  few  to  the  anterior,  and  end  by  ramifying  amongst  the  cells  of 
the  mesial  geniculate  body  (Cajal).  In  its  course  it  traverses  the 
nucleus  of  the  fillef,  which  consists  of  cells  interpolated  amongst  it.s 
fibres  (the  greater  number  in  the  lower  part  near  the  superior  olive), 
amongst  which  some  of  the  tibres  and  many  collaterals  from  them  end. 
The  axons  of  these  cells  trend  inwards  towards  the  raphe.  The  upper 
JiUet  is  continued  upwards  in  the  ventral  part  of  the  tegmentum  towards 
the  thalamus  (p.  409). 

Crusta. — Lateral  and  ventral  to  the  tegmentum  is  seen  on  either  side 
the  white  mass  known  as  the  crusta  or  pes  pedunculi  (figs.  463,  cr.,  464, 
466,  p.p.).  This  is  formed  by  longitudinally  coursing  bundles  of  fibres 
lying  on  the  ventral  aspect  of  each  half  of  the  mesencephalon,  and 
diverging  above  into  the  internal  capsule  of  the  cerebral  hemisphere. 

The  fibres  of  the  crusta  are  continued  below  into  the  so-called 
"pyramid  bundles"  of  the  pons — which  contain,  as  we  have  seen, 
many  more  fibres  than  those  of  the  pyramidal  tract.  This  is  also  the 
case  with  the  bundles  of  the  crusta,  in  which  the  pyramidal  tract 
proper — composed  of  fibres  emanating  from  the  ascending  frontal  and 
paracentral  gyri — is  confined  to  the  middle  three-fifths  (which,  however, 
includes  many  cortico-pontine  fibres),  whilst  the  mesial  fifth  is  mainly 
occupied  by  fibres  passing  from  the  lower  frontal  region  to  the  pons, 
carrying  impulses  to  the  nuclei  of  the  facial  and  hypoglossal ;  and  the 
lateral  fifth  by  fibres  the  origin  and  functions  of  which  are  not  certainly 
known.  But  it  is  probable  that  these  last  are  connected  with  the 
regions  of  the  hemisphere  behind  the  Kolandic  fissure,  especially, 
perhaps,  with  the  temporal  and  occipital  regions ;  and  are  passing 
from  the  pyramidal  cells  of  these  parts  to  end  in  the  nuclei  of  the  pons. 

Substantia  nigra. — The  crusta  is  separated  from  the  tegmentum  by 
a  layer  of  grey  matter  containing  a  number  of  very  deeply  pigmented 
nerve-cells  (substantia  nigra;  figs.  464,  466,  s.n.).  The  substantia  nigra 
receives  many  collaterals  from  the  adjacent  pyramid  bundles  of  the 
crusta.  The  crusta  and  tegmentum,  together  with  the  intervening 
substantia  nigra,  constitute  the  cerebral  peduncle  {pes  or  cms  cerebri). 

Interpeduncular  ganglion. — Between  the  cerebral  peduncles,  just 
where  they  diverge  from  the  mass  of  transverse  fibres  of  the  pons,  is 
seen  close  to  the  ventral  surface  of  the  brain  a  small  mass  of  grey 
matter  containing  a  large  number  of  small  nerve-ceils  with  large  and 
irregular  dendrons,  and  axons  which  are  directed  dorsally  into  the 
tegmentum.  This  is  the  interpediniculur  ffnngli&n  (fig.  464,  g.i.p.).  It 
receives  on  either  side  the  ending  of  the  fasciculus  retroflexus  of  Meynert 
which  comes  from  the  ganglion  of  the  habemda,  a  collection  of  nerve 


406  THE   ESSENTIALS  OF  HISTOLOGY. 

cells  near  the  superior  and  mesial  part  of  the  thalamus,  close  to  the 
commencement  of  the  third  ventricle  (see  fig.  472).  These  ganglia  are 
both  much  better  marked  in  many  of  the  lower  animals  than  in  man. 

Corpora  quadrigemina. — The  prominences  {coUiculi  or  tubercles)  of 
the  corpora  quadrigemina  are  formed  mainly  of  grey  matter. 
Connected  with  each  one  is  a  bundle  of  white  fibres  forming  the 
hrachia  of  the  geniculate  bodies. 


Fig.   465.— Diagram  showing  the  general  structure  of  the  posterior 

CORPORA   QUADRIGEMINA.      (Cajal.) 

A,  principal  mass  of  grey  matter ;  B,  C,  cortical  layer ;  D,  grey  matter  around  Sylvian 
aqueduct ;  K,  decussation  of  superior  peduncles  of  cerebellum ;  a,  b,  c,  d,  fibres  of 
central  acoustic  path  from  lateral  fillet ;  c,  axons  from  cells  of  princij)al  nucleus 
passing  towards  l^racbium  ;  /,  fibres  fi-om  bracliium  passing  into  superficial  layer; 
CI,  fibres  from  fillet  passing  into  superficial  layer  ;  A,  a  fibre  of  fillet  passing  to  centi-al 
grey  matter  of  aqueduct ;  j,  collaterals  from  posterior  longitudinal  bundle  passing 
to  oculo-motor  nucleus ;  I,  axons  of  cells  in  superomosial  part  of  colliculus  curving 
round  grey  matter  of  aqueduct  and  forming  the  deep  white  layer. 

The  posterior  or  inferior  colliculi  consist  of  a  grey  centre  which  is 
enclosed  by  siiperjicial  and  deep  white  layers  (figs.  464,  465).  The  super- 
ficial white  layer  is  derived  mainly  from  the  brachium.  The  fibres  of  the 
fillet  divide  as  they  approach  the  colliculus ;  one  branch  enters  its 
grey  matter  while  the  other  passes  to  the  mesial  geniculate  body. 
In  animals  with  a  highly  developed  sense  of  hearing  all  these  parts 
are  proportionately  developed.  The  deep  white  layer  is  derived  from 
cells  of  the  grey  centre,  but  many  of  the  cells  of  the  latter  send  their 
axons  towards  the  superficial  layer.     The  destination  of  the  fibres  of 


THE   MESENCEPHALON, 


407 


the  deep  white  layer  is  not  certainly  known  ;    some  pass  over  the 
centi'al  grey  matter  of"  the  afiueduct  to  the  opposite  side. 

In  the  anterior  or  superior  coUiculi  lour  hiyers  can  be  distinguished, 
viz.  :  superficially,  a  thin  white  layer  containing  nerve-fibres  and  a  few 
horizontally  disposed  nerve-cells  (fig.  467,  A) ;  next  to  this  a  grey  cap 


Fig.  466.— Section  across  the  mid-brain  through  the  superior  corpora 
QUADRIGEMINA.     Magnified  about  3J  diameters.     (From  a  photograph.) 

c.p.,  posterior  commissure  of  brain;  gt.pi.,  pineal  gland;  c.q.a.,  grey  matter  of  one  of 
superior  corpora  quadrigemina ;  c.g.m.,  mesial  geniculate  body;  e.g. I.,  lateral  geni- 
culate body;  tr.opt.,  optic  tract;  p.p.,  crusta  or  pes  pedunculi ;  p.l.b.,  posterior 
longitudinal  bundle;  Ji,  upper  fillet;  r.n.,  red  nucleus  ;  III.,  issuing  fibres  of  third 
nerve  ;  n.III.,  its  nucleus  ;  I. 'p.p.,  locus  pei-foratus  posticus ;  lS>i,  Sylvian  aqueduct. 

^B)  containing  many  and  various  nerve  cells,  amongst  which  the  termi- 
nations of  the  optic  nerve  (h,  h)  ramify ;  below  this  the  optic  nerve  layer 
(C),  which  is  formed  of  antero-posteriorly  running  fibres  derived  from 
the  optic  tract,  and  ending  as  just  stated  for  the  most  part  in  the  grey 
layer.  This  layer  also  contains  some  nerve-cells.  Lastly  there  is  a 
deep  white  layer,  the  so-called  deep  meilulla,  of  transversely  disposed 
fibres  (D)  derived  partly  from  the  fillet,  but  comprising  many  fibres 
which  are  derived  from  the  cells  of  the  colliculus  itself,  and  a  few  which 


408 


THE   ESSENTIALS   OF   HISTOLOGY. 


are  continued  up  from  the  antero-lateral  ascending  tract  of  the  spinal 
cord.  This  deep  layer  also  contains  a  number  of  large  dendritic 
cells  amongst  the  fibres.  The  superior  corpora  quadrigemina  receive 
through  their  brachia  many  of  the  fibres  of  the  optic  tract,  which 
in  mammals  enter  the  grey  matter  at  the  middle  of  its  thickness  and 
traverse  it  from  before  back,  so  that  in  transverse  sections  of  the  mid 
brain  they  appear  cut  across.     In  liirds  they  form  a  superficial  white 


Fig.  467. — Di.^gkam  showing  the  ch.^kacters  of  the  cells  in  the  grev 

MATTER    OF   THE   ANTERIOR   CORPORA   QUADRIGEMINA.       (Cajal. ) 
M,  portion  of  dorsal  median  groove;  A,  superficial  white  layer;  B,  grey  cap;  C,  optic 

fibre  layer  (upper  grey-white  layer) ;  D,  layer  of  the  fillet  (lower  grey-white  layer). 
«,  a',  marginal  nerve  cells  :  their  axons  are  not  represented  ;  b,  V ,  horizontal  spindle- 
shaped  cells  of  Golyi's  type  II.  ;  c,  c',  small  cells  with  much  branched  dendrons  and 
an  axon  extending  to  the  optic  fibi-e  layer ;  d.  e.  e',  spindle  and  stellate  cells  of  the  grey 
cap,  and  /,  /',  cells  of  the  straturu  opticum,  sending  their  axons  into  the  stratum 
lemnisci;  j/,  </,  cells  of  the  stratum  lemnisci ;  A,  li,  fibres  of  the  optic  nerve  layer 
ending  in  the  grey  and  superficial  white  layers. 

stratum  covering  the  grey  matter,  but  this  is  not  homologous  with  the 
superficial  stratum  of  mammals,  for  the  fibres  in  the  latter  are  not 
derived  directly  from  the  optic  tract.  The  optic  fibres  are  derived 
from  nerve-cells  in  the  retina,  and  as  they  traverse  the  stratum  opticum 
they  pass  obliquely  into  the  grey  matter  (in  a  ventral  direction  in 
birds,  in  a  dorsal  direction  in  mammals)  and  end  in  arborisations 
amongst  its  cells.  The  cells  of  the  grey  matter  are  very  various  in 
form  and  size  (fig.  467).  Most  of  their  axis-cylinder  processes  pass 
ventral  wards.  The  destination  of  all  is  not  certainly  known,  but 
many  appear  to  join  the  anterior  longitudinal  bundle  of  the  opposite 
side.  Others  run  down  on  the  same  side  towards  the  pons  Varolii, 
intermingled  with  the  ascending  fibres  of  the  fillet.  A  certain  number 
of  fibres  which  take  oricrin  in  the  cells  of  the  anterior  colliculi  course 


THE   MESENCEPHALON.  40& 

over  the  central  gvey  matter  which  surruunds  the  Sylvian  aqueduct 
and  sweep  round  this  towards  the  fillet-tract  of  the  opposite  side. 
These  commissural  fibres  are  continuous  in  front  with  those  of  the 
posterior  commissure. 

The  nerve-fibres  of  the  optic  nerve  and  optic  tract  do  not  all  enter 
the  corpora  quadrigemina.  Many,  indeed  the  majority,  pass  into  the 
lateral  geniculate  bodies  and  optic  thalami  to  form  arborisations  there 
(fig.  471).  On  the  other  hand,  axons  from  the  cells  of  these  structures 
pass  to  the  cortex  of  the  brain  (occipital  region). 

As  has  just  been  stated,  many  arcuate  fibres  issue  from  the  grey 
matter  of  the  corpora  quadrigemina  and  pass  obliquely  downwards 
into  the  ventral  part  of  the  mesencephalon  encircling  the  central  grey 
matter.  These  fibres  intercross  in  the  raphe,  where  they  constitute 
the  fountain-decussation  of  Mei/ncrf,  and  after  crossing  constitute  the 
main  mass  of  the  anterior  longitudinal  bundles.  These  are  continued 
into  the  anterior  columns  of  the  spinal  cord ;  they  give  off  collaterals 
to  the  motor  nuclei  of  the  eye-muscles,  and  probably  to  the  motor 
nuclei  generally.  Other  fibres  which  appear  to  belong  to  the  same 
{tectospinal)  system  are  traceable  as  a  distinct  tract  into  the  lateral 
column  of  the  cord  (see  p.  365). 

In  the  cat,  the  anterior  corpora  quadrigemina  receive  a  number 
of  fibres  from  the  pyramidal  tract  in  the  crusta  of  the  same  side,  a 
few  crossing  over  the  aqueduct  to  the  opposite  corpora  quadrigemina 
(Boyce,  Sutherland  Simpson).  But  in  most  animals  the  fibres  which 
pass  from  the  cortex  cerebri  to  the  corpora  quadrigemina  enter  those 
bodies  through  their  respective  brachia. 

No  fibres  are  given  off  from  the  cells  of  the  corpora  quadrigemina 
to  the  cortex  cerebri. 

The  optic  nerves. — The  only  sensory  nerves  which  are  immediately 
connected  with  the  mid-brain  are  the  second  or  optic.  Their  origin  is 
from  the  large  nerve-cells  of  the  ganglion  of  the  retina  (p.  455). 
The  nerve  leaves  the  globe  of  the  eye  at  its  posterior  aspect,  passes 
through  the  optic  foramen  to  the  base  of  the  brain,  and  joins  the  nerve 
of  the  opposite  side  to  form  the  optic  chiasma  (fig.  471).  Of  the  fibres 
which  enter  the  chiasma,  those  from  the  inner  (or  nasal)  two-thirds 
of  the  retina  cross  to  the  optic  tract  of  the  opposite  side,  while  the. 
remaining  third,  comprising  the  fibres  from  the  temporal  part  of  the 
retina,  pass  along  the  lateral  border  of  the  chiasma  to  the  tract  of 
the  same  side.  In  the  optic  tract  they  are  continued  to  the  parts  of 
the  brain  where  they  have  their  terminal  arborescences,  viz.,  the 
external  geniculate  body  and  the  adjoining  posterior  part  of  the 
thalamus*  (pulvinar)  and  the  anterior  corpora  quadrigemina.     A  certain 


410  THE   ESSENTIALS  OF  HISTOLOGY. 

number  of  the  fibres  of  the  optic  nerve  bifurcate  on  reaching  the 
chiasma,  and  the  branches  pass  one  into  each  optic  tract  (Cajal). 

The  hlires  which  pass  to  the  anterior  corpora  quadrigemina  are  much 
finer  than  those  to  the  corpora  geniculata.  It  is  probable  that  the 
former  furnish  the  path  for  reflex  movements  of  the  pupil,  etc.,  and 
the  latter  the  i)ath  for  visual  impressions,  since  the  lateral  corpora 
geniculata  and  pulvinar  thalami  are  directly  connected  with  the  visual 
cortex  in  the  occipital  lobe,  while,  as  already  stated,  no  such  direct 
connection  obtains  between  that  cortex  and  the  anterior  corpora 
quadrigemina. 

■  A  small  bundle  of  fibres  (transverse  peduncular  bundle)  leaves  the 
optic  tract  as  it  enters  the  mid-brain  and  passes  round  the  cerebral 
peduncle  to  lose  itself  in  the  mesial  part  of  the  tegmentum  near 
the  fillet.  Its  destination  appears  to  be  a  small  nucleus  siti;ated 
near  the  red  nucleus.  Its  fibres  degenerate  after  enucleation  of  the 
opposite  eyeball. 

The  optic  tracts  and  chiasma  also  contain  the  fibres  of  v.  Giidden's 
commissure,  which  connects  the  posterior  corpora  quadrigemina,  but 
these  fibres  appear  to  have  no  relation  to  the  visual  function. 

There  are  present  in  the  optic  nerve  and  tract  a  few  fil)res  which 
originate  in  the  nerve-centres — where  is  not  known — and  terminate 
in  the  retina. 

Motor  nerves. — The  motor  nerves  arising  from  the  mid-brain  are  the 
third  and  fourth.  The  position  of  their  nuclei  and  their  mode  of  exit 
have  been  already  described  (pp.  401,  402). 

Posterior  commissure. — Immediately  in  front  of  the  corpora  quadri- 
gemina, visible  in  the  roof  of  this  part  of  the  mid-brain,  is  the  posterior 
commissure.  This  consists  of  fibres  which  arise  in  a  nucleus  at  each 
side  of  the  Sylvian  aqueduct  and  which  pass  across  the  middle  line 
dorsal  to  the  central  grey  matter  and  then  turn  ventralwards  and 
caudalwards  to  pass  down  in  the  tegmentum  lateral  to  the  posterior 
longitudinal  bundle,  which  is  partly  reinforced  by  the  fibres  in  question. 
The  posterior  commissure  extends  into  the  region  of  the  third 
ventricle. 

THE   THALAMENCEPHALON. 

The  optic  thalamus  (fig.  468,  th.)  which  lies  at  the  side  of  the 
third  ventricle  and  forms  part  of  the  floor  of  the  lateral  ventricle, 
is  covered  externally  by  a  layer  of  white  fibres,  most  marked  next 
to  the  internal  capsule.  Fibres  from  the  latter  pass  into  the  thalamus 
and  serve  to  connect  it  with  the  hemisphere. 

The    o'rey    matter    of    the    thalamus    is    partially   subdiVided   by 


THE   THALAMENCEPHALON. 


411 


ail  ol)li(iue  white  luiuiiia  into  a  smaller,  mesial,  and  a  larger 
lateral  itiideus ;  these  contain  a  large  number  of  small  nerve-cells. 
Anteriorly  another  portion  of  grey  matter  (anterior  nuclem)  is  divided 
off  in  a  similar  way ;  this  contains  comparatively  large  nerve-cells. 
These  nuclei  are  themselves  formed  of  several  groups  of  cells  having 
difierent  connections,  many  of  which  still  re({uire  elucidation. 


Fig.  468. — Hokizumal  skction  through  the  optic  thalamus  and  corpus 

STRIATUM.  (Natural  size. ) 
V.I.,  lateral  ventricle,  its  anterior  cornu  ;  c.c,  corpus  callosum  ;  g.l.,  septum  lucidum  ; 
a.f.,  anterior  pillars  of  the  fornix;  v3,  third  ventricle;  th.,  thalamus  opticus; 
St.,  stria  medullaris;  nc,  nr'.,  nucleus  caudatus,  and  nl.,  nucleus  leuticularis  of  the 
corpus  striatum  ;  i.e.,  internal  capsule  ;  g,  its  angle  or  genu  ;  nc'.,  tail  of  the  nucleus 
caudatus  appearing  iu  the  descending  cornu  of  the  lateral  ventricle  ;  cl.,  claustruiu  ; 
/,  island  of  Reil. 

The  thalamus  receives  the  terminal  branches  of  the  fibres  of  the 
upper  fillet,  continued  from  the  cells  of  the  opposite  nuclei  of  Goll  and 
Burdach  (spino-thalamic  tract) ,  of  the  central  path  of  the  fifth  cranial 
nerve  of  the  opposite  side,  and  some  fibres  from  the  superior  cerebellar 
peduncle  of  the  opposite  side  ;  besides  the  fibres  of  the  optic  tract  which 
pass  to  the  external  geniculate  body  and  pulvinar  thalami. 

From  the  cells  of  the  thalamus  nerve-fibres  pass  in  every  direction 
into  the  white  matter  of  the  hemisphere,  and  eventually  to  the  cortex 
(figs.  437,  469).    From  the  outer  part  they  tend  especially  into  the 


412  THE   ESSENTIALS  OF  HISTOLOGY. 

occipital  region,  assisting  to  form  the  central  visual  tract  which  passes 
to  the  visual  cortex.  From  the  inner  and  deeper  part  they  converge 
towards  the  subthalamic  region  and  many  are  collected  into  the  ansa 
lenticularis  (see  p.  415),  by  which  they  pass  into  the  nucleus  lenticularis, 
while  others,  as  already  stated,  enter  the  corona  radiata  and  thus  reach 
the  cortex  of  the  hemisphere.  These  fibres  from  the  thalamus  to  the 
cortex  probably  form  the  third  and  last  link  in  the  chain  of  sensory 


Fig.  469. — Diagram  of  the  coxxectioxs  ok  the  thalamus  with  the  ascexd- 
ixg  fibbes  of  the  oth  xerve,  axd  of  the  upper  fillet  ox  the  oxe 

HAXD,  AXD  WITH  THE  CORTEX  CEREBRI  OX  THE  OTHER.   (Cajal. ) 

A,  B,  C,  D,  E,  various  nuclei  in  thalamus  ;  1,  afferent  fibres  passing  to  manimillary  body 
F;  G,  tract  of  upper  fillet  endirjg  in  A  (at  c),  and  giving  collaterals  to  D  (posterior 
nucleus) ;  H,  central  tract  from  sensory  nucleus  of  5th  ;  T,  cortex  cerebri ;  V,  visual 
cortex;  II,  anterior  colliculus  ;  J,  optic  chi:isma ;  S,  optic  fibres  ;  K,  hippocampus. 

a,  fibres  from  cortex  to  thalamus,  ending  at  e  ;  b,  fibres  from  cells  in  thalamus  (d)  to 
cortex  ;  /',  fibres  from  lateral  geniculate  body  and  thalamus  to  visual  cortex,  ending 
at  g  in  stria  of  Gennari. 

neurones,  the  second  being  formed  by  the  neurones  of  the  fillet  and  the 
first  by  the  neurones  of  the  sensory  roots.  On  the  other  hand,  the 
thalamus  receives  fibres  from  the  cortex  and  from  the  corpus  striatum, 
which  end  amongst  its  cells. 

Attached  to  the  optic  thalamus  below  and  behind  are  the  two 
geniculate  bodies  (fig.  470)  which  at  first  sight  appear  to  be  both 
connected  with  the  optic  tract,  although  only  the  outer  one  actually 
receives  optic  fibres.  The  inner  or  mesial  geniculate  body  receives 
fibres  from  the  central  auditory  tract  through  the  lateral  fillet.     Of 


THK   THALAMENCEPHALON. 


413 


the  geniculate  Ixxlies  the  outer  or  hiteral  lias  a  lamellated  structure 
consisting  of  alternating  layers  of  grey  and  white  matter,  the  white 
layers  being  composed  partly  of  the  entering  optic  hbres  and  partly  of 
fibres  emerging  from  the  grey  matter  and  passing  to  the  central  optic 
path,  Avhilc the  greysul)stance  contains  very  mimerous  nerve-cellsamongst 


Fig.  470.~Fi(a'RE  showing  thk  olfactoky  tkacts  axd  their  roots  :  the 

OPTIC    CHIASMA     AND    OPTIC    TRACTS  :     THE    GENICULATE    BODIES    AND    THE 

PULVINAR  THALAMI.     (Edinger. ) 
The  pons  is  cat  through  at  the  anterior  part,  and  the  section  shows  the  Sylvian  aqueduct, 
the  fillet  (liiiiiinn  laquearis),  superior  cerebellar  peduncles,  etc.  (see  fig.  459).      The 
corpora  mamniillaria  are  partly  concealed  by  the  pons  ;   between  and  in  front  of 
them  is  seen  the  infundibuhim  and  pituitarj'  body. 

•which  the  fibres  of  the  optic  tract  end  in  complex  arborisations.  From 
these  cells  axons  arise  and  join  a  bundle  of  fibres  which  enters  the  white 
matter  of  the  hemisphere  above  and  along  with  the  internal  capsule, 
-and  passes  to  the  visual  area  of  the  cortex  (central  visual  tract)  Some 
of  the  fibres  from  the  corpus  geniculatum  externum,  as  they  enter  the 
A'isual  tract,  send  branches  downwards  towards  the  tegmentum. 


414 


THE   ESSENTIALS  OF  HISTOLOGY. 


The  ganglion  of  the  habenula  (fig.  472,1'/')  is  a  small  collection 
of  nerve-cells,  which  lies  at  the  posterior  part  of  the  thalamus  on  each 
side,  near  the  roof  of  the  third  ventricle.  This  ganglion  receives  on 
the  one  hand  the  fibres  of  the  habenula  or  stria  medullaris,  and  on  the 
other  hand  gives  off  from  its  cells  the  fibres  which  form  the  fasciculus 
refrqfle.vus  (fig.  496),  which  pass  downwards  to  the  interpeduncular 
ganglion  (p.  405).  The  two  ganglia  of  the  habenulse  are  joined  by 
a  white  commissure. 

The  corpora  mammillaria  (fig.  470)  are  seen  at  the  base  of  the  brain 
immediately  below  the  posterior  part  of  the  third  ventricle.     Each  is. 


Fig.  471. 


-Diagram  to  show  the  probable  course  and  relations  of 

THE   optic   fibres.  1 


composed  of  white  matter  externally  and  grey  matter  internally.  It 
receives  fibres  from  the  anterior  pillar  of  the  fornix  of  the  same  side  ; 
these  fibres  arise  from  cells  in  the  hippocampus  and  end  in  the  mammil- 
lary  body.  According  to  Edinger  some  fibres  from  the  olfactory 
tract  pass  directly  to  it.  The  axons  of  its  cells  bifurcate,  one  branch, 
the  coarser,  passing  into  the  anterior  and  upper  part  of  the  thalamus  in 


^  Only  single  fibres  are  shown  emerging  from  the  anterior  qiiadrigeminal  and 
external  geniculate  bodies,  continuing  the  course  of  the  two  fibres  from  correspond- 
ing points  in  the  retinae.  This  is  merely  to  simplify  the  diagram  and  is  not 
intended  to  imply  that  the  retinal  impressions  are  fused  in  those  situations. 


THE   THALAMENCEPHALON. 


415 


the  bundle  of  Vicq  d'Azyr,  and  the  other  into  the  tegmentum  of  the 
mid-brain  in  v.  Gudden's  bundle.  The  cori)ora  manimillaria  form  part 
of  the  central  olfactory  apparatus  (fig.  490). 

Subthalamic   region. — The  tegmentum  of  the  crus  cerebri   is  pro- 
longed below  the  thalamus  opticus,   and  between   it  and  the  internal 


n^t: 


Fig.  472. — Section  taken  obliquely  through  the  optic  thalamus  and 
internal  capsule  showing  some  of  the  strands  of  fibres  of  the 
SUBTHALAMUS.     (Magnified  2i  diameters.) 

T/i.,  thalamus;  -0.111.,  third  ventricle;  t.,  taenia,  or  attachment  of  epithelial  roof  of 
ventricle;  sir.,  stria  medullaris  or  habenula ;  </',  ganglion  of  the  habennla  ;  n.i., 
mesial  nucleus  of  thalamus;  o-pt.,  optic  fibres  jjassing  into  pulvinar  of  thalamus; 
zi.,  zona  incerta,  from  which  fibres  are  seen  emerging  and  sweeping  as  the  ansa 
lenticularis,  a. I.,  round  the  internal  capsule,  c.i.,  to  pass  towards  the  lenticular 
nucleus ;  c.s.,  corpus  subthalamicum  ;  /.,  anterior  pillar  of  fornix  passing  backwards 
to  corpus  mammillare  ;  F.A.,  bundle  of  Vicq  d'Azyr,  passing  upwards  and  foi-wards 
from  corpus  rnammillai  e  into  thalamus  ;  g,  group  of  nerve  cells,  probably  belonging 
to  the  nucleus  of  the  corpus  mammillare  ;  x,  fasciculus  retroflexus. 


capsule,  into  a  mass  of  grey  substance,  with  longitudinally  and 
obliquely  crossing  white  bundles,  which  is  known  under  the  name  of 
suhthalanms  (fig.  472).  Its  deepest  part  contains  a  lens  shaped  mass  of 
grey  matter  prolonged  forwards  from  the  substantia  nigra,  known  as 
the  corpus  subthalamicum  (Luys).     A  mass  of  fibres  sweeps  round  this 


416  THE   ESSENTIALS   OF   HISTOLOGY. 

and  round  the  internal  capsule  passing  between  the  thalamus  and  the 
nucleus  lenticularis,  this  is  known  as  the  ansa  lenticular  is. 

The  pineal  gland  or  epiphysis  cerebri  (fig.  461),  which  is  developed 
in  the  roof  of  the  third  ventricle,  but  passes  backward  between  the 
anterior  corpora  quadrigemina,  is  composed  of  a  number  of  tubes  and 
saccules  lined  and  sometimes  almost  filled  with  epithelium,  and  con- 
taining deposits  of  earthy  salts  {brain  sand).  (Similar  deposits  may 
also  occur  in  other  parts  of  the  brain,  especially  in  the  pia-mater.) 
The  follicles  are  separated  from  one  another  by  vascular  connective 
tissue  derived  from  the  pia-mater,  and  along  with  the  vessels  are 
numerous  nerve-fibres  of  sympathetic  type  (Cajal).  No  true  nerve- 
cells  can  be  seen,  although  there  are  a  number  of  cells  similar  in  general 
appearance  to  the  "granules"  of  the  cerebellum,  but  apparently  without 
axons.  In  some  animals  (ox)  striated  muscular  fibres  have  been  met 
with. 

In  the  chameleon  and  some  other  reptiles,  the  pineal  is  better  developed, 
and  is  connected  by  nerve-fibres  with  a  rudimentary  median  eye  of  inverte- 
brate type,  placed  upon  the  upper  surface  of  the  head. 

The  pituitary  body  or  gland  {hypophysis  cerebri)  is  connected  with  the 
third  ventricle  by  the  infundibulum.  It  consists  of  two  lobes,  a  large 
anterior  and  a  smaller  posterior.  The  structure  of  the  pituitary  body 
has  already  been  described  (p.  224). 


THE   CEREBELLUM.  417 


LESSONS    XLIY.   and    XLV. 
STIU'CTCRI-:  OF  THE  CEREBELLUM  AND  CEREBRUM. 

1.  Sections  of  the  cerebellani  vertical  to  the  surface,  {a)  across  the  direction 
of  tlie  hxniiricTe,  (/>)  parallel  with  the  laiuinte. 

2.  Sections  across  the  whole  of  one  hemisphere  of  the  cerebrum  of  a  monkev 
passing  through  the  third  ventricle. 

3.  Vertical  sections  of  the  cerebral  cortex  : — one  across  the  ascending 
frontal  and  ascending  parietal  gyri,  another  fi'om  the  occipital  lobe  (calcarine 
region),  another  across  the  superior  temporal  gyrus  and  island  of  Eeil,  and 
one  across  the  hippocampal  gyrus  and  hippocampus. 

4.  Transvei"se  sections  of  the  olfactory  tract  and  bulb. 

In  all  these  preparations  make  sketches  under  a  low  power  of  the  general 
arrangement  of  the  grey  and  white  matter,  and  also  of  the  nerve-cells  in  the 
grey  matter.     Sketch  some  of  the  details  under  a  high  power. 

The  preparations  are  made  in  the  same  way  as  those  of  the  spinal  cord. 
Other  preparations  should  be  made  by  the  Golgi  method  to  exhibit  the 
relation  of  the  cells  to  one  another.  Such  preparations  have  been  already 
partly  studied  (Lessons  XVIL  and  XVIII). 


The  Cerebellum. 

The  cerebellum  is  composed  of  a  white  centre,  and  of  a  grey  cortex. 
Both  e.xtend  into  all  the  folds  or  laminae,  so  that  when  the  laminae 
are  cut  across,  an  appearance  is  presented  of  a  white  arborescence 
covered  superficially  by  grey  matter.  The  white  matter  is  in  largest 
amount  in  the  middle  of  each  cerel)ellar  hemisphere.  There  is  here 
present  a  peculiar  wavy  lamina  of  grey  matter,  similar  to  that  in  the 
olivary  body,  and  known  as  the  nucleus  dentatus  (fig.  473,  n.d.).  This 
receives  numerous  nerve-fibres  from  the  cells  of  Purkinje  of  the  cortex, 
■which  end  by  arborising  around  its  cells.  The  latter  give  off  axons 
Avhich  become  the  fibres  of  the  superior  cerebellar  jjeduncles,  and 
for  the  most  part  end  in  the  opposite  red  nucleus,  but  some  pass  beyond 
this  into  the  subthalamic  region.  The  dentate  nucleus  also  receives 
collaterals  from  fibres  of  the  inferior  peduncle  (Cajal). 

Other  isolated  grey  nuclei  lie  in  the  white  matter  of  the  middle  lobe 
■over  the  roof  of  the  4th  ventricle  and  constitute  collectively  the  nuclei 
of  Stilling.  The  most  important  of  these  appears  to  be  the  niideiis  tecti 
{s.  fasfigii)  (fig.  473).  This  receives  many  of  the  ascending  fibres  of  the 
vestibular  nerve  (p.  385)  and  collaterals  from  the  spinocerebellar  tracts, 
and  gives  origin  to  a  bundle  of  fibres  which  crosses  to  the  opposite  side 

•2d 


418 


THE   ESSENTIALS  OF  HISTOLOGY. 


and  descenfls  in  the  mesial  part  of  the  restiform  body  to  the  reticular 
formation  of  the  medulla  oblongata  (Risien  Russell). 

The  grey  matter  of  the  cerel)elluni  appears  essentially  of  similar 
structure  throughout  the  whole  extent  of  the  cortex.  It  consists  of 
two  layers.  The  inner  one  (that  next  to  the  white  centre)  is  composed 
of  a  large  number  of  very  small  nerve-cells  intermingled  with  a  few 
larger  ones  and  some  neuroglia-cells  {granule  layer,  fig.  474,  d).  The 
outer  one  is  thicker,  and  is  formed  chiefly  of  fine  nerve-fibres  (fig.  476,  A) 


Choroid  g/^i^,^ 
jji-ex-us 


SI 


Fig.    473.— Section   across   the   cerebellum    and   medulla   oblongata 

SHOWING    the    position    OF    THE    NUCLEI    IN    THE    WHITE    CENTRE    OP    THE- 
CEREBELLUM.      (Stilling. ) 
n.d.,  nucleus  dentatus  cerebelli ;  i.c.-p.^  fibres  of  superior  peduncle;    com,  com',  com", 
commissural  fibres  ;    A',  rootlet  of  vagus  ;  XII,  rootlet  of  hypoglossal  nerve. 

with  small  nerve  cells  scattered  through  it  {molecular  layer,  fig.  474,  h). 
Into  its  outer  part  processes  of  the  pia-mater  conveying  blood-vessels 
pass  vertically,  and  there  are  also  in  this  part  a  number  of  long 
tapering  neuroglia-cells,  somewhat  like  the  Miillerian  fibres  of  the 
retina  (fig.  479,  gP.  See  also  fig.  191,  p.  161).  Lying  between 
the  two  layers  of  the  grey  matter  is  an  incomplete  stratum  of  large 
flask-shaped  cells  (fig.  474,  c)  {cells  of  Fnrkinje,  fig.  475).  Each  of  these 
gives  off"  from  its  base  a  fine  process  (axon),  which  becomes  the  axis- 
cylinder  of  one  of  the  medullated  fibres  of  the  white  centre,  while 
from  the  opposite  pole  of  the  cell  large  ramified  processes  (dendrons) 
extend  into  the  superficial  layer  of  the  grey  matter. 


THE   CEREBELLUM. 


419 


The  (loiidroiis  of  the  cells  of  I'nikiiijc  spread  out  in  planes  trans- 
verse to  the  direction  of  the  lamellae  of  the  organ,  so  that  they 
present  a  different  appearance  according  to  whether  the  section  is 
taken  across  the  lamella-  or  along  them  (compare  figs.  476  and  477). 
These   dendrons  are    invested   at   their  attachment    to  the  cell,   and 


Fig.  474. — Section  of  cortex  of  cerebellum.    (Sankey.) 

a,  pia-mater ;  b,  external  layer;  c,  layer  of  corpuscles  of  Purkinje  ;  (',  inner  or  granule 
layer  ;  f,  medullary  centre. 

for  some  extent  along  their  branchings,  by  basket-works  formed  by 
the  terminal  arborisations  of  certain  fibres  (climbing  or  tendril  fibres) 
of  the  medullary  centre  (fig.  479,  cl.f.).  The  body  of  the  cell  of 
Purkinje  is  further  invested  by  a  felt-work  of  fibrils  formed  by  the 
arborisation  of  axis-cylinder  processes  of  nerve-cells  {basket-cells)  in  the 


420 


THE   ESSENTIALS   OF   HISTOLOGY. 


outer  layer  of  the  grey  matter  (figs.  478  ;  479,  /').  Each  cell  has 
therefore  a  double  investment  of  this  nature,  one  covering  the 
dendrons,  the  other  the  bod}^  of  the  cell  and  extending  along  the 
commencement  of  the  axon. 


Fig.   475.— a  cell  of  pcrkinje  of  the  cerebellum,   shown  by  golgi's 
METHOD.      (Cajal.) 

a,  axon  ;  h,  collateral  from  axon  ;  c,  d,  arborisation  of  dendrons. 

The  granules  of  the  inner  layer  of  grey  matter  are  mostly  small 
nerve-cells,  each  with  a  few  dendrons  penetrating  amongst  the  other 
granules,  and  an  axon  which  is  directed  between  the  cells  of  Purkinje 
into  the  outer  layer.  After  penetrating  a  variable  distance  into  this 
layer  it  bifurcates,  and  its  two  branches  pass  in  opposite  directions  at 
right  angles  to  the  main  stem,  and  parallel  to  the  direction  of  the 
lamella  (fig.  476).  What  ultimately  becomes  of  the  branches  is  not 
known.  In  sections  cut  across  the  lamella  the  cut  ends  of  these  fibres 
give  a  finely  punctated  appearance  to  the  outer  layer  (fig.  477). 


THE   CEREBELLUM. 


421 


Figs.  476  and  477.— Sections  of  cortex  cerebelli  stained  by  golgi's 

METHOD.     (Oajal. ) 

Fio.  476.-Section  made  in  the  direction  of  the  lamina.     Fig.  47r.-Section  taken  across 

A,  outer^or'molecular  layer  ;  B,  inner  or  granule  layer  ;  C\  medullary  centre 

n    cormiscles  of  Purkinie  •    b,  small  granules  of  inner  layer ;   c,  a  protoplasmic  process 

'  7de   dron)  of  a  gran   le  ;  -'   nerve-fibre  process  of  a  granule  passing  into  the  molecular 

ayer,  -^ere  it^bifurcates  and  become^s  a  longitudinal  fib,^  ^"^  f^-^Aj^f^J?T^ 

tudinal  fibres  are  cut  across  and  appear  as  dots) ;  e,  bifurcation  of  another  fibre  ,  g,  a 

granule  lying  in  the  white  rentre. 


Fig    478  —Basket-work  of  fibres  around  two  cells  of  pdrkinje. 

(Cajal.) 
a    axis-cylinder  or  nerve-fibre  process  of  one  of  the  corpuscles  of  Purkinje ;   b,  fibres 
'     prolonged  over  the  beginning  of  the  axis-cylinder  process ;  c,  branches  of  the  nerve- 
fibre  processes  of  cells  of  the  molecular  layer,  felted  together  around  the  bodies  of 
the  coi-puscles  of  Purkinje. 


422 


THE   ESSENTIALS   OF  HISTOLOGY. 


Some  of  the  cells  of  the  granule  layer  are  far  larger  than  the  others, 
and  send  their  much-branching  axons  amongst  the  smaller  granules 
(cells  of  Golgi,  fig.  479,  G).     Besides  these,  other  large  "granules"  have 


Fig.  479.— Diagrammatic  section  of  cerebellum  to  show  the  characters 

AND  relations  OF  THE  CELLS  AND  FIBRES  MET  WITH  IN  THE  SEVERAL  LAYERS 
AS  EXHIBITED  BY  THE  CHROMATE  OF  SILVER  METHOD.      (After  KolHker.) 

P,  a  cell  of  Purkinje  ;  G,  a  cell  of  Golgi ;  h,  a  basket-cell ;  m,  m,  other  cells  of  the  molecular 
Ltyer  ;  gr,  granules  ;  p,  a  nerve-fibre  of  the  white  substance  derived  from  a  Purkinje 
cell ;  m.f.,  "  moss  "-fibres  ;  cl.f.,  a  climbing  fibre  ;  nl^,  gl-,  gP,  types  of  neurogUa-ceUs. 

been  noticed  by  Cajal,  occurring  both  in  the  granule  layer  and  in  the 
white  centre,  with  long  axons  passing  into  the  white  matter  of  the 
cerebellum.     These  are,  however,  only  rarely  met  with. 

Ramifying  amongst  the  cells  of  the  granule  layer  are  peculiar  fibres 
derived  from  the  white  centre,  and  characterised  by  having  pencils  of 


THE   C'KREI^KLLUM. 


423 


fine  short  bmnches  at  intervals  like  tufts  of  moss  (fig.  479,  iiif).  These 
have  been  termed  by  Cajal  the  moss-fibre.<f ;  they  end  partly  in  the 
granide  layer,  iiailly  in  tlie  niolocular  layer. 


left  cortex 
cerebr 


Rigbt  cortex 
cerebelli 


JXuclcns  doiitatus 
cerebelli 


Kye  muscle 


Pyramidal  tract 
fibres 


Skeletal  muscle 


Fig.  480. 


-Diagram  of  the  connections  of  the  cerebellum  through  its 
PEDUNCLES.     (Cajal.) 


The  neuroglia  of  the  cerebellum  is  peculiar  in  containing,  besides  the 
ordinary  branched  and  unbranched  neuroglia  cells  (fig.  479,  gl^,  gP), 
cells  which  possess  long  parallel  processes  which  extend  through  the 
molecular  layer  to  be  attached  to  the  surface  of  the  lamellae  (gP).  (See 
also  fig.  191.)  The  cell-bodies  of  these  lie  at  about  the  same  level  as 
those  of  Purkinje's  cells. 


424  THE   ESSENTIALS   OF  HISTOLOGY. 

The  peduncles  of  the  cerebellum  have  been  already  studied  in  connec- 
tion with  the  medulla  oblongata,  pons,  and  mid-brain.  The  inferior 
pe'luncle  (restiform  body)  is  composed  of  ascending  fibres  derived  from 
the  dorsal  spino-cerebellar  tract,  from  both  olivary  nuclei — but  chiefly 
from  that  of  the  opposite  side  :  perhaps  also  from  the  nuclei  of  the 
gracile  and  cuneate  funiculi,  from  cells  and  nuclei  of  the  reticular 
formation  of  the  medulla  oblongata  and  from  the  sensory  nuclei  of 
the  cranial  nerves,  especially  of  the  vestibular  nerve.  The  fibres  of  the 
spinocerebellar  tract  occupy  the  outer  part  of  the  peduncle.  Most 
of  the  fibres  of  the  inferior  peduncle  pass  to  the  vermis,  crossing  to 
the  opposite  side  over  the  fourth  ventricle,  but  before  doing  so  they 
give  off"  strong  collaterals  to  the  hemisphere  of  the  same  side.  The 
inferior  peduncle  also  contains  a  small  bundle  of  fibres  descending 
from  the  nucleus  tecti  of  the  opposite  side  to  the  medulla  oblongata 
(Risien  Russell)  which  bends  round  the  superior  peduncle  to  join  the 
inferior  peduncle,  its  fibres  lying  between  those  of  the  superior 
peduncle  and  Gowers'  bundle.  The  inferior  peduncle  contains  a  very 
small  nucleus  of  grey  matter  (Dejerine)  which  is  almost  completely 
concealed  amongst  the  mass  of  white  fibres. 

The  middle  peduncle  is  formed  of  fibres  from  the  cells  of  the  nuclei 
pontis  which  are  passing  to  the  opposite  hemisphere  of  the  cerebellum. 

The  superior  peduncle  is  formed  of  fibres  which  mostly  take  origin 
in  the  corpus  dentatum  cerebelli,  but  some  are  said  to  arise  in  the 
hemisphere  and  pass  through  this.  The  superior  peduncles  decussate 
in  the  mid-brain  across  the  raphe,  and  their  fibres  then  bifurcate  into 
ascending  and  descending  branches.  The  ascending  branches  pass 
forwards  and  end  in  the  red  nucleus,  but  some  fibres  go  past  this 
into  the  ventral  part  of  the  thalamus.  The  descending  branches  are 
traceable  into  the  dorsal  part  of  the  reticular  formation  of  the  pons. 
According  to  Cajal  they  are  connected  with  the  motor  iniclei  of  the 
pons,  medulla  oblongata,  and  spinal  cord  (fig.  480).  The  superior 
peduncle,  as  it  issues  from  the  hemisphere,  is  joined  by  the  bundle 
of  Gowers,  which  runs  over  it,  and  passes  backwards  along  its  mesial 
border  to  the  vermis. 

STRUCTURE   OF  THE   CEREBRL^I. 

The  grey  matter  of  the  cerebral  cortex  is  described  as  if.  composed 
of  a  number  of  layers,  but  they  are  not  sharply  marked  off"  from  one 
another,  and  they  vary  in  relative  development  in  diflerent  regions  of 
the  cortex.  The  cells  are  for  the  most  part  of  a  pyramidal  shape 
(fig.  481).  The  following  layers  are  generally  distinguishable,  but  in 
some  parts  of  the  cortex  a  larger  number  can  be  made  out : 


THE   CEREBRAL   CORTEX. 


42.' 


1.  A  peripheral  stratum  (molecular  ov  plexifffrm  layer,  figs.  481,  4.S2,  1) 
containing  scattered  nerve-cells  and  many  neuroglia-cells.     In  the  most 


Fig.  481.— Ascending  parietal  coxvolutiox,  golgi  method.     (Cajal.) 

1,  plexif onn  layer ;  2,  small  pyramids ;  3,  medium  pyramids ;  4,  superficial  large  pyramids ; 

5,  granules  ;  6,  deep  large  pyramids  ;  7,  deep  medium  pyramids. 


426  THE   ESSENTIALS  OF  HISTOLOGY. 

superficial  part  of  this  layer,  immediately  .under  the  pia-mater,  is  a 
thin  stratum  of  medullated  nerve-fibres,  and  besides  these  the  layer 
contains  a  large  number  of  fibres,  many  of  which  are  ramified. 
They  are  largely  derived  from  the  deeper  nerve-cells  of  the  cortex. 
Intermingled  with  these  fibres  are  a  certain  number  of  ramified 
nerve-cells,  which  have  several  long  horizontally  disposed  dendrons 
and  a  long  axon,  all  of  which  terminate  by  arborisation  within  the 
superficial  layer  {horizontal  cells  of  Cajal)  (fig.  482).  Besides  these, 
others  of  a  somewhat  similar  character  but  with  short  axis-cylinder 
processes  occur  in  this  layer. 

2.  A  layer  of  closely  set  small  pyramidal  nerve-cells,  several  deep 
(layer  of  small  pyramiih,  fig.  481,  2).  This  layer  also  contains  other 
kinds  of  cells  (fig.  491,  k,  f,  g). 

3.  A  layer  of  medium-sized  pyramidal  cells  less  closely  set,  with 
small  granule-like  cells  amongst  them  {layer  of  medium-sized  jxyramids, 
fig.  481,  3;  fig.  491,  J,  H,  K). 

4.  A  laj^er  of  larger  pyramidal  cells  {superficial  large  pijramids, 
fig.  481,  4). 

5.  A  layer  of  small  irregular  cells  {small  stellate  cells,  fig.  481,  5). 
The  large  pyramids  may  extend  down  into  this  layer. 

6.  A  layer  of  still  larger  pyramids  {deep  large  pyramids,  fig.  481,  6). 
In  the  motor  region  of  the  cortex,  which  in  man  is  confined  to  the 
ascending  frontal  gyrus  and  paracentral  lobule,  pyramidal  cells  of 
very  large  size  (giant  cells)  occur,  and  are  disposed  in  small  clusters 
or  "  nests "  (Betz,  Bevan  Lewis).  The  fibres  of  the  pyramidal  tract 
arise  from  these  giant  cells.  In  some  parts  of  the  cortex  this  layer 
is  absent  or  is  blended  with  the  next  layer. 

7.  A  layer  of  medium-sized  pyramidal  cells  {deep  medium  pyramids, 
fig.  481,  7). 

8.  A  layer  of  small  scattered  cells,  many  of  a  fusiform  shape 
{pjolymorphous  layer).  This  layer  lies  next  to  the  white  centre.  In  the 
island  of  Eeil  it  is  considerably  developed,  and  is  separated  from  the 
rest  of  the  grey  matter  by  a  layer  of  white  substance.  It  is  here 
known  as  the  claustrum,  and  on  that  account  the  layer  is  sometimes 
termed  the  daustral  layer. 

Some  authorities  describe  the  cortex  as  consisting  only  of  three  layers, 
viz.  :  the  molecular  layer,  the  layer  of  pyramids,  and  the  layer  of  polymor- 
phous cells  ;  others  of  four,  five,  etc.,  up  to  nine.  As  a  matter  of  fact,  the 
complexity  and  the  number  of  distinct  layers  vary  in  ditferent  regions.  The 
pyramidal  cells  of  the  cortex  are  so  termed  from  the  shape  of  the  cell-body, 
which  usually  gives  off  several  dendrons  from  tlie  base  of  the  pyramid  and 
one  large  dendi'on  from  its  apex.  This  process  extends  to  the  plexiform 
layer,  on  approaching  which  it  breaks  up  into  numerous  ramifications  which 
have  a  general  vertical  direction  and  extend  almost  to  the  outer  surface. 


Fig.  482.— Diagram  showing  the  relations  of  some  of  the  cells  in  the 

CEREBRAL  CORTEX.     (Barker,  after  Starr,  Strong  and  Learning.) 
1,  plexiform  layer  with  cells  of  Cajal ;   2,  small  (rf,  e)  and  middle  sized  (,/)  pyramids; 

3,  large  pyramids  (f/,  </,  k) ;  also,  m,  cell  with  axon  passing  towards  the  surface,  but 
soon  ramifying  ;  n,  li,  cell  of  Golgi's  second  type,  with  axon  ramifying  in  the  adjacent 
grey  matter  :  one  of  these  belongs  to  the  kind  termed  by  Cajal  "double-brush"  cells  ; 

4,  polymorphous  cells,  of  which  p  ends  its  axon  towards  the  surface  and  q  its  axon 
into  the  medullary  centre,  5,  which  contains  also  the  axons  of  the  pyramids  ;  r,  r, 
afferent  fibres,  ending  in  the  cortex. 


428  THE   ESSENTIALS   OF   HISTOLOGY 

This  apical  dendron  is  beset,  both  in  its  undivided  part  and  in  its  branches, 
by  minute  spinous  projections  (as  seen  in  specimens  prepared  by  the  Golgi 
method).  Tliese  projections  are  believed  In-  some  authors  to  be  retractile 
(amoeboid)  and  to  be  the  means  of  effecting  (or  breaking)  nervous  connection 
with  affei'ent  fibres  ;  since  they  are  in  some  preparations  prominent,  in  others 
hardly  visible  ;  or  the  dendrons  are  entirely  free  from  them,  and  have  an  even 
outline  or  may  be  slightly  moniliform.  All  the  pyramidal  cells  have  a  single 
axon,  which  is  usually  directed  towards  the  medullary  centre,  of  which  it 
forms  one  of  the  fibres  ;  but  the  axon  sometimes  curves  back  and  passes  out- 
wards again,  ending  in  arborisations  in  one  of  the  other  layers.  Intei'mingled 
with  the  pyramids  and  polymorphous  cells  are  two  other  kinds  of  cells, 
viz.  :  (1)  cells  with  axis-cylinder   process   ramifying    near    the    cell-body  ; 

these  occur  in  all   the   layers  (fig. 
a  h  491),  .and  (2)  small   cells   sending 

their  axons  towards  the  plexiform 
layer  (Martinotti),  these  are  found 
chiefly  in  the  deeper  layers  of  the 
cortex. 

From  the  white  centre  bundles 
of  medullated   nerve-fibres   pass 

Fig.  483. -Sections  of  cerebral  con-       i"   vertical    streaks   through   the 
VOLUTIONS.    (After  Bailiarger.)  deeper  layers  of  the  grey  matter, 

(Natural  size.)  i  J  o     j  ' 

t      4.V.      ■  .V,     1     1   f  *.i,„„„i^„.i„<.         to  lose  themselves  amongst  the 

a,  from  the  neighbourhood  of  the  calcanne  y^        ^  j, 

^^^'u^''.Ti^^•°°'^'.°r?'''"'''^'''^''  r"'*''^'         pyramidal    cells     of    the    more 

visible  (the  hne  of  German) ;  b,  ordinary  i  J 

type,  with  the  superficial  white  layer  and  superficial  layers  (figS.   487,  490). 

outer  and  inner  lines  of  Bailiarger  shown.  i  j  \    o  '  / 

Many  large  fibres  however  are 
seen  running  not  A^ertically  but  obliquely  into  the  grey  centre  from  the 
white  matter.  Most  of  the  vertically  disposed  fibres  are  the  nerve-fibre 
processes  of  the  pyramidal  and  polymorphous  cells,  and  therefore  take 
origin  in  the  cortex ;  others,  including  the  oblique  fibres  just  men- 
tioned, are  passing  into  the  cortex,  probably  from  the  thalamus,  to  end 
amongst  the  cells  of  the  several  layers  in  free  arborisations  (fig.  484). 

Besides  these  vertical  strands  of  fibres  there  are  others  which  lie  in 
planes  parallel  to  the  surface  of  the  cortex,  and  which  are  derived 
partly  from  the  fibres  which  enter  the  cortex  from  the  white  matter, 
partly  from  the  collaterals  which  are  given  off"  from  the  axis-cylinder 
processes  of  the  cortical  cells  themselves.  The  planes  in  w^hich  these 
fibres  occur  are  (1)  near  the  surface  in  the  plexiform  (molecular) 
layer :  this  superficial  stratum  of  white  fibres  is  best  marked  in  the 
hippocampal  region  ;  (2)  in  the  layer  of  medium-sized  pyramids  :  here 
the  fibres  give  the  appearance  of  a  whitish  line  in  the  section  of  the 
grey  matter  (outer  line  of  Bailiarger,  fig.  483  b).  There  is  a  particularly 
dense  plexus  of  fibres  in  this  situation  in  certain  regions  of  the  cortex, 
especially  the  occipital  lobe  (in  man  in  the  convolutions  bounding  the 
calcarine  fissure),  producing  a  very  distinct  line,  here  known  as  the  line 
of  Gennari  (fig.  483,  a).    This  plexus  of  nerve-fibres  is  in  intimate  associa- 


THE   CEREBRAL  CORTEX. 


429 


tion  withj  certain  large  and  small  stellate  cells  which  are  characteristic 
of  the  visual  region.  (3)  In  most  regions  of  the  l)rain,  in  the  plane  of 
the  layer  of  large  pyramids,  another  white  line  is  seen  ;  this  is  known 
as  the  inner  line  of  BaiUunjer.  The  planes  in  which  these  white  lines 
are  found  are  characterised  especialh'  in  the  occipital  and  temporal 
lobes,  by  the  presence,  amongst  the  pyramids,  of  great  numbers  of 


Fig.    484.— PrEPARATIOX    SHOWIXG    SOJIE   of   the    .-iFFERENT    FIBRES    OF    THE 

ASCEXniXG  FRONTAL  GYRUS— HUMAN.  (Cajal.) 
A,  part  of  second  layer  ;  £,  layer  of  medium-sized  pyramids  with  close  terminal  plexus  ; 
C  to  D,  intermediate  plexus  of  horizontal  fibres ;  £,  deep  plexus  of  large  oblique 
afferent  fibres  ;  n,  h,  afferent  fibres  arborising  in  the  layer  of  middle  pyramids, 
amongst  which  they  form,  along  with  fibres  derived  from  cells  in  the  cortex  itself, 
the  dense  plexus  which  is  shown  in  the  left  half  of  the  figure.  The  efferent  fibres 
are  not  shown  in  this  figure. 

small  nerve-cells,  amongst  which  the  white  fibres  of  the  layers  ramify 
and  probably  terminate. 

The  axis-cylinder  processes  of  the  pyramidal  cells  pass  into  the 
white  centre.  Here  some  of  them  are  continued  into  the  corpus 
callosum,  and  through  this  to  the  cortex  of  the  opposite  hemisphere 
{commissural  fibres) ;  others  form  associalion-fibres  which  eventually  pass 
again  into  the  grey  matter  of  other  parts  of  the  same  hemisphere ; 


?'| 


6 


«  f  f  (  I! 


I.  iH!V 


.  /• 


Fig.  485.  Fig.  486.  Fig.  487. 

Fig.  485. — Section  of  ascending  parietal  gyrus  of  man,  stained  by 
Nissl's  method.     (Cajal.) 
1,   plexiform  layer ;    2,   small  pyramids ;    3,   medium    pyramids ;    4,   superficial   large 
pyramids;   5,  small  stellate  cells  (granules);  6,  deep  large  and  medium  pyramids; 
7,  fusiform  ceUs. 
Fig.  486.— Section  of  ascending  frontal  gyrus  (motor  cortex),  stained 
BY  Xissl's  method.     (Cajal.) 
1  to  6  as  before  ;  a,  c,  small  cells  amongst  the  pyramids  ;   b,  a  large  pyramid  ;  d,  a  giant 

cell  of  Betz. 

Fig.  487. — Section  of  one  of  the  motor  convolutions  (man), 
stained  by  Weigert's  method.     (Cajal.) 


''^  '■')  m^G 


Fig.  488. 


'-'mi' 


.I*  V2 


■•'6  <>■?«■  •"^"^'jr^ri 


t< 


*!.. 


Fig.  489. 


Dg^)^. 


::V  /  i\  - 


/-.'' 


Fig.  490. 

Fig.  488. — Calcarine  (visual)  cortex  of  man.     (Cajal.)    Nissl's  method. 
1,  plexiform  layer;    2,   small  pyramids;    3,  medium  pyramids;    4,  large  stellate  cells 
(characteristic  of  this  part  of  the  cortex) ;   .5,  small  stellate  cells;   6,  a  deep  plexiform 
layer,  containing  some  small  pjramids ;    7,  large  pyramids  ;   8,  layer  of  small  and 
medium  pyramids  with  bent  ascending  axons ;  H,  fusiform  cells. 

Fig.  489. — Sectio.n'  of  first  temporal  gyrus  (acou.stic  cortex  of  man), 

STAINED   BY    NiS.SL'S    METHOD.       (Cajal.) 
1,  plexiform  layer ;  2,  layer  of  small  pyramids  ;  3,  superficial  medium  pyramids ;  4,  large 
pyramids  ;  5,  small  stellate  cells  (granules) ;  6,  deep  medium  pyramids  ;  7,  fusiform 
cells. 


Fig. 


490.— Section  of  the  fir.st  temporal  gyrus  (man),  stained  by 
"Weigert's  method.     (Cajal.) 


432  THE   ESSENTIALS   OF   HISTOLOGY. 

whilst  others  again,  especially  those  of  the  largest  pyramidal  cells, 
extend  downwards  through  the  corona  radiata  and  internal  capsule. 
These  include  the  projection-fibres  of  the  pyramidal  tract  and  of  the 
cortico-pontine  tract.  As  the  projection  fibres  pass  through  the  grey 
and  white  matter  of  the  hemisphere  they  give  off  collateral  fibres  to 
the  adjacent  grey  matter,  to  the  corpus  callosum,  and  to  the  corpus 
striatum  and  optic  thalamus,  and  some  probably  end  in  these  masses  of 
grey  matter.  According  to  Cajal,  in  the  brain  of  man  as  compared 
with  the  lower  mammals,  there  is  a  marked  preponderance  of  cells  of 
Golgi's  type  II.  (with  short  axis-cylinder  ramifying  near  the  cell  body). 
Such  cells  are  most  numerous  in  the  layer  of  stellate  cells  and  in 
the  laj^er  of  small  pyramids. 

Special  features  of  certain  parts  of  the  cortex. — There  is,  as  already 
stated,  a  great  amount  of  variation  met  with  in  the  relative  extent  of 
development  of  the  above  layers.  This  is  exemplified  in  the  accom- 
panying drawings  by  Cajal  (figs.  48-5  to  488)  of  certain  convolutions 
in  the  human  brain.  From  these  it  will  be  seen  that  smaller-sized 
cells  prevail  in  some  regions  of  the  cortex  (occipital,  temporal) ;  larger 
and  fewer  cells  in  others  (frontal,  parietal,  limbic).  Nests  or  groups 
of  very  large  "giant"  cells  are  characteristic  of  the  "motor"  region 
(ascending  frontal  gyrus  and  paracentral  lobule  in  man  and  anthropoid 
apes) ;  these  cells  give  oingin  to  the  fibres  of  the  pyramidal  tract,  and 
undergo  Nissl  degeneration  when  these  fibres  are  severed.  The 
occipital  region  (in  man,  the  neighbourhood  of  the  calcarine  fissure) 
is  especiall}^  characterised  b}'-  the  great  numbers  of  small  stellate  cells 
and  by  the  presence  in  the  layer  superficial  to  them  of  a  stratum  of 
very  large  stellate  cells  with  long  spreading  dendrons  (fig.  488,  4) : 
amongst  these  stellate  cells  (small  and  large)  the  optic  fibres  from 
the  lateral  geniculate  bodies  ramify.  A  preponderance  of  small 
stellate  cells  is  also  seen,  but  to  a  less  extent,  in  sections  of  the 
temporal  lolje ;  to  a  still  less  extent  in  the  prefrontal  and  parietal 
regions.  The  first  temporal  gyrus  is  characterised  by  the  presence 
in  nearly  all  the  layers,  but  especially  the  deepest,  of  special  large 
cells  with  widely-spreading  dendrons  and  an  axon  passing  towards 
the  white  substance  but  giving  off"  many  collaterals  in  the  grey  matter. 
There  are  also  very  many  cells  of  Golgi's  type  II.  with  axis  cylinder 
ramifying  in  a  most  complex  manner  near  the  cell-body,  mainly  in  a 
plane  vertical  to  the  surface.  The  cortex  of  the  insula  has  special 
cells  similar  to  those  in  the  first  temporal  gyrus,  and  is  further 
characterised  by  the  peculiar  spindle-shape  of  many  of  the  large 
pyramids. 

The  size  and    ruimber  of  the    medullated    fibres  vary  in   different 


THE   CEREBRAL   CORTEX.  433 

regions.  In  some  they  are  large  and  numerous  (motor  {)art  of  ascending 
frontal,  calcarine  area,  hippocampal  area),  in  others  fine  and  much  less 
conspicuoiis  (g3'rus  fornicatus,  temporal  area,  parietal  area,  prefrontal 
area,  insula  and  lobus   pyriformis),  whilst  an   intermediate  condition 


Fig.  4i>l. — .Superficial  layers  of  motor  cortex  of  child,  Golgi  method.     (Cajal.) 

A,  B,  C,  cells  of  Cajal  in  plexiform  laj'er ;  D  to  K,  cells  of  type  ii.  of  Golgi  (with 
axons  ramifying  near  cell-body);  H,  J,  "double-brush."  types  of  celL 

presents  itself  in  the  occipital  area  (except  the  calcarine  region),  the 
transverse  temporal  gyri  and  superior  temporal  gyrus,  the  part  of  the 
frontal  immediately  in  front  of  the  motor  region  and  the  ascending 
frontal.  These  differences  have  been  employed  by  Campbell  in 
attempting  to  diff'erentiate  the  functions  of  the  various  cerebral 
regions  by  a  comparison  of  their  structure. 


THE   KHINENCEPHALON. 

The  rhinenceplialon  (olfactory  region  of  the  telencephalon),  on 
account  of  the  peculiarities  of  its  structure,  its  importance  in  most 
a.ninials,  and  the  fact  that  it  has  been  the  part  of  the  telencephalon  to 

2e 


434  THE  .ESSENTIALS  OF  HISTOLOGY 

appear  first  in  phylogenetic  development  (archipallhim  of  Elliott-Smith) 
merits  a  special  description,  although  in  man  and  primates  general!}', 
and  in  some  other  (microsmatic)  mammals,  it  is  reduced  to  a  compara- 
tively rudimentary  condition.  On  the  other  hand,  in  the  so-called 
osmatic  (macrosmatic)  mammals  there  is  a  large  hollow  olfactory  bulb 
forming  the  anterior  termination  of  a  thick  olfactory  lobe  which 
broadens  out  behind,  where  it  is  continuous  with  the  hippocampal 
gyrus  and  hippocampus.  The  whole  forms  a  pyriform  mass,  which 
is  separated  from  the  rest  of  the  cortex  {neopallium)  by  a  well-marked 
fissure — the  limbic  fissure — and  has  special  connections  through  the 
anterior  commissure  and  fornix  with  other  parts  of  the  brain  on  the 
same  and  on  the  opposite  side. 

In  man  the  rhinencephalon  consists  anteriorly  of  the  small  olfactmy 
bulb  from  which  the  thin  olfactory  tract  extends  backwards  to  the 
grey  matter  at  the  base  of  the  brain  and  to  the  hippocampal  region. 
Posteriorly  the  cortex  of  the  rhinencephalon  is  doubled  in  so  as  to 
form  a  projection,  the  hippocatiipus  inajor,  into  the  descending  cornu 
of  the  lateral  ventricle  :  its  edge  here  thins  ofl"  and  is  continued  merely 
as  an  epithelial  covering  to  the  choroid  plexus  of  the  pia-mater,  which 
is  invaginated  into  the  ventricle.  At  this  thin  edge  the  white  matter 
comes  to  the  surface  as  the  fimbria  (which  is  continuous  with  the 
fornix) ;  lying  along  this  is  the  small  and  half-concealed  dentate  gyrus, 
which  is  formed  by  the  sharp  bending  of  the  grey  matter,  and  which  is 
traceable  round  into  the  hippocampus  major  (from  this  it  is  separated 
by  the  hippocampal  fissure),  while  this  again  is  directly  continuous 
externally  with  the  gyrus  hippocampi.  The  olfactory  lobe  (tract)  is- 
connected  directly  with  the  hippocampal  region  by  its  lateral  root, 
whilst  a  mesial  root  passes  into  the  anterior  commissure  and  connects  it 
with  the  rhinencephalon  of  the  opposite  side.  The  structure  and  con- 
nections of  all  these  parts  as  they  occur  in  man  may  be  briefly  alluded  to. 

In  the  region  of  the  hippocampus  major  (figs.  492,  493),  the  cortex 
is  simpler  in  structure  than  elsewhere,  and  in  the  hippocampus  major 
itself,  which  is  an  infolded  part  of  the  cortex,  the  pyramids  are  reduced 
to  a  single  layer  of  large  cells  lying  in  the  deeper  portion  and  sending 
their  apical  dendrons  as  long  fibres  into  the  plexiform  layer.  The 
plexiform  layer  and  the  superficial  white  stratum  which  overlies  it  are 
both  very  strongly  marked,  the  plexiform  layer  having  a  distinctly 
reticular  aspect,  due  partly  to  neuroglia  cells,  partly  to  the  arborescence 
of  the  dendrons  of  the  pyramids :  the  plexiform  layer  is  here  termed 
stratum  laciniosura ;  internal  to  it  near  the  dentate  gyrus  is  a  layer  of 
closely  packed  small  cells  termed  stratum  granulosum.  The  pyramidal 
cells  lie  close  to  the  white  layer  known  as  the  alveus.     This  is  the  part 


THE   RHINENCEPHALON. 


4:$-) 


of  the  hippocampus  seen  within  the  ventricle,  and  represents  the  white 
matter  of  the  hemisphere.  The  alveus  is  prolonged  externally  into  the 
Jiiiihria,  in  which  its  fibres  become  longitudinal  in  direction  and  are 
continued  into  part  of  the  fornix. 


Fig.    492.— Section    across    the    hippocampus    major,    dentate    fissure, 

DENTATE   FASCIA   AND    FIMBRIA.       (W.    KraUSe.) 

D,  fascia  dentata,  or  dentate  convolution  ;  F,  fimbria,  composed  of  longitudinal  fibres 
here  cut  acro.ss  ;  H,  medullary  centre  of  the  hippocampal  gyrus  prolonged  around 
the  hippocampus,  as  the  so-called  alveus,  into  the  fimbria;  1,  layer  of  large  pyra- 
midal cells;  -2,  their  processes  (stratum  radiatum);  3,  stratum  granulosum  ;  4, 
plexiform  layer  (stratum  laciniosum) ;  5,  superficial  white  layer ;  6,  nerve-cells  of 
fascia  dentata  ;  7,  stratum  granulosum  of  fascia  dentata  ;  S,  plexiform  layer  of  the 
fascia  dentata. 


In  the  dentate  gyrus  (fascia  dentata,  figs.  492,  493,  d)  the  pyramidal 
cells  (6)  are  arranged  in  an  irregularly  radiating  manner,  occupying  the 
centre  of  the  convolution,  and  surrounded  by  a  ring  of  closely  packed 
small  cells  {stratum  granulosum,  fig.  492,  7).  External  to  these  is  a  thick 
plexiform  layer,  occupied  by  interlacing  fibres  (stratum  laciniosum). 

The  anterior  part  of  the  hippocampal  gyrus,  which  is  known  as 
the  lobus  pyriformis,  and  receives  the   lateral  root  of  the  olfactory 


436  THE   ESSENTIALS  OF  HISTOLOGY. 

tract,  is  characterised  by  the  presence  in  the  plexiform  layer  of 
peculiar  nests  of  nerve  cells.  The  cells  in  these  nests  are  of  two 
types,  viz.,  large  polymorphous  cells  and  small  pyramidal  cells,  each 
being  confined  to  its  own  nest.  This  part  of  the  cortex  is  regarded 
by  Cajal  as  the  true  olfactory  region.     In  some  animals  the  anterior 


Fig.  493. — Hippocampal  kegiox,  Golgi  method.     (Cajal.) 

A,  B,  hippocampal  gyrus ;  C,  hippocampus  major  ;  D,  dentate  gj-rus  ;  E,  fimbria ; 
F.  white  matter  of  hippocampal  gyrus  ;  G,  lateral  ventricle ;  H,  fibres  of  corpus 
callosum. 

«,  efferent  fibres  of  hippocampal  gyrus ;  h,  afferent  fibres  of  hippocampal  gyrus  ;  c,  afiferent 
fibres  of  hippocampus  and  dentate  gyrus  ;  d,  others  perforating  <rrey  matter  of  hippo- 
campal gyrus;  c,  others  cut  obliquely  (from  sphenoidal  part  of  brain);  /.  fibi-es  of 
alveus ;  p.  h,  cells  of  hippocampus  major  sending  their  axons  into  the  alveus  and 
towards  the  fimbria ;  i,  k,  collaterals  from  these  axons  passing  to  the  molecular 
layer ;  )•,  afferent  fibres  of  alveus.  The  arrows  indicate  the  probable  course  of  the 
nerve  impulses. 

perforated  space  forms  a  distinct  prominence  of  the  cortex  (tuberculum 
olfactorium)  and  this  is  also  characterised  by  cell-nests  (islets  of  Calleja). 
They  also  occur  in  the  cortex  of  the  hippocampal  fissure. 

The   olfactory   tract    is   an    outgrowth   of    the    brain   which    was 
originally  hollow,  and  remains  so  in  many  animals ;  but  in  man  the 


THE  OLFACTORY   BULB. 


437 


cavity  has  become  obliterated,  and  the  centre  is  occupied  by  neuro- 
glia, containing  no  nerve  cells.  Outside  the  central  neuroglia  lies 
the  white  or  medullary  substance,  consisting  of  bundles  of  longi- 
tudinal white  fibres.  Most  externally  is  a  thin  superficial  layer  of 
neuroglia. 

The  olfactory  bulb    (fig.   494)  has   a  more   complicated   structure. 
Dorsally    there    is   a    flattened    ring   of   longitudinal    white    bundles 


li 


~J ;) 


Fig.  494. — Section  across  a  part  op  the  olfactory  bulb.     (Henle.) 

1,  3,  bundles  of  very  fine  transversely  cut  nerve-fibres,  forming  the  flattened  medullary 
ring,  inclosing  the  central  neuroglia,  2  :  this  ring  is  the  anterior  continuation  of  the 
olfactory  tract ;  5,  white  layer  with  numerous  small  cells  (granules) ;  6,  mitral-cell 
layer ;  7,  layer  of  olfactory  glomeruli ;  S,  layer  of  olfactory  nerve-fibres,  bundles  of 
which  are  seen  at  *  passing  through  the  cribriform  plate  of  the  ethmoid  bone. 

inclosing  neuroglia  (1,  2,  3),  as  in  the  olfactory  tract,  but  below  this 
ring  several  layers  are  recognised  as  follows  : 

1.  A  lohite  or  medullary  layer  (fig.  494,  4,  5),  characterised  by  the 
presence  of  a  large  number  of  small  cells  ("granules")  with  reticu- 
lating bundles  of  medullated  nerve-fibres  running  longitudinally 
between  them. 

2.  A  layer  of  large  nerve-cells  (6),  with  smaller  ones  ("granules") 
intermingled,  the  whole  embedded  in  an  interlacement  of  fibrils  which 
are  mostly  derived  from  the  cell-dendrons.     From  the  shape  of  most 


438 


THE   ESSENTIALS  OF  HISTOLOGY. 


Fig.  495. — Diagram  to  show. the  relations  of  cells  and  fibres  in  the 
olfactory  bulb. 

olf.c,  olfactory  cells  of  M.  Schiiltze  in  the  olfactory  mucous  membrane,  sending  their 
basal  processes  as  non-medullated  nerve-fibres  into  the  deepest  layer  of  the  olfactory 
bulb  (ol/.n.) ;  (/I,  olfactoi'y  glomeruli  containing  the  terminal  arborisations  of  the 
olfactory  fibres  and  of  processes  from  the  naitral  cells;  mc,  mitral  cells,  sending 
processes  down  to  the  olfactory  glomeruli,  others  laterally  to  end  in  free  ramifica- 
tions in  the  nerve-cell  layer,  and  their  axis-cylinder  processes,  a,  a,  upwards,  to 
turn  sharply  backwards  and  become  fibres  of  the  olfactory  tract  (n.tr.).  Numerous 
collaterals  are  seen  coming  off  from  these  fibres  ;  n',  a  nerve-fibre  of  the  olfactory 
tract  ending  in  a  free  ramification  in  the  olfactory  bulb. 


CO 

^Mi5su»\E  or 

Ml 

'POCAWPI 

^> 

K^G. 

r^LPON  or  The 

\ 

A'O     HASENOLA 

a^^ 

^ 

i. 

Fig.  496. — Diagram  of  the  olfactory  path  in  the  brain.  To  simplify 
the  diagram  the  various  divarications  of  the  olfactory  path  have  been 
represented  by  branchings  of  individual  fibres,  although  in  some  cases  the 
divarication  is  brought  about  bj'  the  turning  aside  of  bundles  of  entire  fibres. 


THE   OLFACTORY   BULB.  439 

of  the  large  cells  of  this  layer  (fig.  495,  7n.c.)  it  has  been  termed  the 
"  mitral "  layer.  These  cells  send  their  axons  upwards  into  the  next 
layer,  and  they  eventually  become  fibres  of  the  olfactory  tract  and 
pass  along  this  to  the  base  of  the  brain,  giving  off  numerous  collaterals 
into  the  bulb  as  they  run  backwards. 

3.  The  lai/er  of  olfadori/  ghmervU  (fig.  494,  7  ;  fig.  495,  fjl.).  This 
consists  of  rounded  nest-like  interlacements  of  fibrils  which  are  derived 
on  the  one  hand  from  the  terminal  arborisations  of  the  non-medullated 
olfactory  fibres  which  form  the  subjacent  layer,  and  on  the  other  hand 
from  arborisations  of  dendrons  of  the  large  "mitral"  cells  of  the  layer 
above.  There  are  also  a  few  small  nerve-cells  immediately  external  to 
and  extending  within  the  glomeruli  (periglomerular  cells).  These  belong 
to  Golgi's  type  II.,  and  appear  to  connect  neighbouring  glomeruli. 

4.  The  layer  of  olfactory  nerve-fibres  (fig.  494,  8 ;  fig.  495,  olf.n.). 
These  are  all  non-medullated,  and  are  continued  from  the  olfactory 
fibres  of  the  olfactory  mucous  membrane  of  the  nasal  fossae.  In 
this  mucous  membrane  they  take  origin  from  the  bipolar  olfactory 
cells  which  are  characteristic  of  the  membrane  (see  Lesson  XLV.  fig. 
528),  and  they  end  in  arborisations  within  the  olfactory  glomeruli, 
where  they  come  in  contact  with  the  arborisations  of  the  mitral  cells. 
The  relations  of  the  olfactory  cells  and  fibres  to  the  mitral  cells,  and 
the  continuation  of  the  axis-cylinders  of  the  latter  upwards  and  back- 
wards in  the  olfactory  tract,  are  shown  in  the  accompanying  diagrams 
(figs.  495,  496).  Besides  these  centripetal  nerve-fibres  there  are  a 
certain  number  of  centrifugal  fibres  which  end  by  ramifying  in  the 
olfactory  bulb  amongst  the  mitral  cells. 

As  is  seen  in  fig.  496,  many  of  the  fibres  of  the  olfactory  tract  pass 
to  the  hippocampal  region  of  the  brain,  terminating  by  arborescence  in 
the  grey  matter  (molecular  layer)  of  the  base  of  the  olfactory  lobe  in 
the  region  of  the  anterior  perforated  space,  as  well  as  in  that  of  the 
uncus  and  the  hippocampal  gyrus.  Fibres  are  also  given  off  from  the 
olfactory  tract  to  the  anterior  commissure  which  proceed  to  the  oppo- 
site tract  and  bulb.  Besides  these  the  anterior  commissure  contains 
many  fibres  which  are  passing  from  the  hippocampal  region  of  one  side 
to  the  corresponding  region  on  the  opposite  side  of  the  brain.  From 
the  p3'ramid -cells  of  the  base  of  the  olfactory  lobe  and  hippocampal 
gyrus  fibres  pass  to  the  grey  matter  of  the  hippocampus,  and  from  the 
pyramid-cells  of  the  hippocampus  others  proceed  by  way  of  the 
fimbria  and  fornix  to  the  hippocampus  of  the  other  side,  to  the  sub- 
callosal gyrus  and  septum  lucidum,  to  the  ganglion  of  the  habenula, 
and  finally  by  the  anterior  pillar  of  the  fornix  to  the  corpora 
mammillaria. 


440  THE   ESSENTIALS  OF   HISTOLOGY. 

CORPUS   STRIATUM. 

Besides  the  grey  matter  of  the  cerebral  cortex  the  cerebral  hemi- 
spheres conceal  in  their  deeper  parts  certain  other  masses  of  grey 
substance  (fig.  497).  The  principal  of  these  are  the  corpus  striatum 
{nucleus  caudatus,  n.c,  and  nucleus  lenticularis,  n.l.)  and  optic  thalamus 
(th.).  Between  them  run  the  bundles  of  white  fibres  which  are 
passing  downwards  to  the  crus  cerebri,  forming  a  white  lamina 
termed  the  internal  capsule.  Above  the  level  of  these  nuclei  the 
internal  capsule  expands  into  the  medullary  centre  of  the  hemisphere. 
Below  the  optic  thalami  are  the  prominent  ganglia  known  as  corpora 
albicantia  or  mammillaria.  Of  these  the  optic  thalami  and  corpora 
mammillaria  have  already  been  described. 

The  nucleus  caudatus  of  the  corpus  striatum  is  composed  of  a  reddish- 
grey  substance  containing  cells  some  with  long,  others  with  short  axis- 
cylinders  ;  some  of  the  former  being  very  large.  It  receives  fibres 
from  the  part  of  the  internal  capsule  which  separates  it  from  the 
nucleus  lenticularis,  and  next  to  the  lateral  ventricle  it  is  covered  by 
a  thin  layer  of  neuroglia,  and  over  this  by  the  epithelium  of  the  cavity 
(ependyma). 

The  nucleus  lenticularis,  which  corresponds  in  position  internally 
with  the  island  of  Reil  externally,  is  divided  by  two  white  laminse  into 
three  zones.  It  is  separated  from  the  nucleus  caudatus  and  optic 
thalamus  by  the  internal  capsule  (fig.  497,  i.e.),  which  consists  of  the 
bundles  of  medullary  fibres  which  are  passing  between  the  white 
centre  of  the  hemisphere  and  the  crus  cerebri ;  it  receives  on  its  inner 
side  many  white  fibres  from  the  capsule,  and  these  impart  to  it  a 
radially  striated  aspect.  Many  of  the  nerve-cells  of  the  nucleus 
lenticularis  contain  yellow  pigment.  The  fibres  of  the  ansa  lenticularis 
appear  to  arise  from  some  of  them,  but  the  exact  course  and  destination 
of  these  fibres  is  not  known. 

The  internal  capsule  (fig.  497),  which  is  continued  below  into  the 
crusta  (pes)  of  the  crus  cerebri,  consists  mainly  of  projection-fibres, 
which  are  derived  from  the  cortex  cerebri,  and  are  passing  down  to 
the  thalamus,  mid-brain,  pons,  medulla  oblongata,  and  spinal  cord. 
A  horizontal  section  across  the  internal  capsule  shows  it  to  be 
bounded  laterally  by  the  lenticular  nucleus,  mesially  by  the  caudate 
nucleus,  the  stria  medullaris,  and  the  optic  thalamus.  Its  section 
shows  a  sharp  bend — the  genu.  The  fibres  from  the  motor  region  of 
the  cortex  (pyramidal  tract)  pass  down  in  the  part  of  the  capsule 
extending  from  the  genu  as  far  as  the  posterior  limit  of  the  lenticular 
nucleus.     In  this  area  the  fibres  for  the  head  and  eyes  are  massed 


INTERNAL  CAPSULE. 


441 


chieHy  in  the  anterior  part :  those  of  the  lower  liml)  in  the  posterior 
part,  and  those  of  the  face,  arm,  and  trunk  occupy  intermediate  posi- 
tions from  before  backward,  in  the  order  named  (Bcevor  and*fHorsley), 
but  without  beino;  strictly  confined  to  definite  zones. 


Fig.  497.— Horizontal  section  through  the  optic  thalamus  and  corpus 
STRIATUM.     (Natural  size. ) 

V.I.,  lateral  ventricle,  its  anterior  cornu  ;  c.c,  corpus  callosvim  ;  s.l.,  septum  lucidum  ; 
a./.,  anterior  pillars  of  the  fornix;  v3,  third  ventricle;  th.,  thalamus  opticus; 
St.,  stria  medullaris;  nc,  nc'.,  nucleus  caudatus,  and  nl.,  nucleus  lenticularis  of  the 
corpus  striatum  ;  i.e.,  internal  capsule  ;  g,  its  angle  or  genu  ;  me'.,  tail  of  the  nucleus 
caudatus  appearing  in  the  descending  cornu  of  the  lateral  ventricle  ;  cl.,  claustrum  ; 
/,  island  of  Reil. 


The  fibres  from  the  cortex  to  the  thalamus  lie  mainly  in  the  anterior 
limb  of  the  capsule,  while  the  afferent  fibres  from  the  thalamus  to  the 
cortex  occur  in  the  posterior  part  of  the  posterior  limb,  but  extend 
forwards  so  as  to  mingle  with  the  descending  fibi-es  just  referred  to 
as  belonging  to  the  pyramidal  tract. 

The  membranes  of  the  brain  are  similar  in  general  structure  to  those 
of  the  spinal  cord.  The  dura  mater  is,  however,  more  closely  adherent 
to  the  inner  surface  of  the  bony  enclosure  than  is  the  case  in  the 
vertebral  canal.  The  arachnoid  is  in  many  places  close  to  the  dura 
mater,  and  separated  by  a  wide  subarachnoid  space  (which  is  bridged 


442  THE   ESSENTIALS  OF   HISTOLOGY. 

across  by  finely  reticulating  bands  of  areolar  tissue)  from  the  pia 
mater.  In  the  vicinity  of  the  longitudinal  sinus,  small  rounded 
elevations  (arachnoidal  villi,  Pacchionian  glands)  project  into  the  dura 
mater,  and  even  Vjecome  embedded  in  the  skull  itself.  The  pia  mater 
is  closely  adherent  to  the  surface  of  the  brain,  and  dips  into  all  the 
sulci,  but  without  forming  actual  folds  (Tuke).  In  it  the  blood-vessels 
ramify  before  passing  into  the  substance  of  the  brain,  and  they  are 
accompanied,  as  they  thus  enter  the  cerebral  substance,  by  prolonga- 
tions of  the  pia  mater,  which  do  not,  however,  closely  invest  them,  but 
leave  a  clear  space  around  each  vessel,  presumably  for  the  passage  of 
lymph  (perivascular  space).  The  capillary  network  is  much  closer  in 
the  grey  than  in  the  white  matter. 


THE   EYELIDS.  443 


LESSOXS  XLVI.,  XLVIL,  and  XLVIII. 

STRUCTURE   OF   THE  EYELIDS   AND    OF   TEE  FARTS    OF 
THE  EYEBALL. 

1.  Sections  of  the  eyelid  vertical  to  its  surfaces  and  transverse  to  its  long 
axis. 

Notice  the  long  sacculated  Meibomian  glands  lying  in  dense  connective 
tissue  close  to  the  conjunctival  surface,  their  ducts  opening  at  the  margin  of 
the  lid.  External  to  these  the  small  fibres  of  the  orbicularis  palpebrarum  are 
cut  across  ;  a  few  of  the  fibres  of  the  muscle  lie  on  the  conjunctival  side  of 
the  duct.  A  short  distance  from  the  Meibomian  gland  may  be  observed  a 
tolerably  large  sebaceous  gland  ;  outside  this  again  are  the  eyelashes.  In 
the  skin  covei"ing  the  outer  surface  of  the  eyelid  a  few  small  hairs  may  be 
seen.  At  the  attached  part  of  the  eyelid  are  some  bundles  of  involuntary 
muscular  fibres  cut  longitudinally  in  the  section,  and  in  the  upper  eyelid  the 
fibrous  attachment  of  the  elevator  muscle  may  be  observed  attached  to  the 
dense  connective  tissue. 

Make  a  general  sketch  under  a  low  power. 

2.  Sections  through  the  posterior  part  of  an  eyeball.  These  sections  will 
show  the  relative  thickness  of  the  several  coats  and  the  layers  of  which  each 
coat  is  formed.  Sections  which  pass  through  the  point  of  entrance  of  the 
optic  nerve  will  also  exhibit  the  manner  in  which  the  nerve-fibres  pierce  the 
several  coats  to  reach  the  inner  surface  of  the  retina.  The  modifications 
•which  are  found  in  the  neighbourhood  of  the  yellow  spot  may  be  made  out 
in  sections  through  that  region  ;  but  they  must  be  taken  from  the  human 
eye,  or  from  that  of  the  monkey. 

3.  Sections  of  the  anterior  half  of  an  eyeball.  Tliese  sections  should  pass 
through  the  middle  of  the  cornea.  The  lens  may  be  left  in  situ,  but  this 
renders  the  preparation  of  the  sections  and  the  mounting  of  them  diflicult 
on  account  of  the  extreme  hardness  which  is  imparted  to  the  lens-tissue  by 
alcohol.^ 

In  these  sections  make  a  general  sketch  under  a  low  power,  showing  the 
relations  of  the  several  parts  one  with  another  ;  and  study  carefully,  and 
sketch  in  detail,  the  layers  of  the  cornea,  the  junction  of  the  cornea  and 
sclerotic,  the  ciliary  muscle,  the  muscular  tissue  of  the  iris,  the  mode  of 
suspension  of  the  lens,  and  the  pars  ciliaris  retinai. 

4.  Mount  in  glycerine  thin  tangential  sections  of  a  cornea  stained  with 
chloride  of  gold  by  Cohnheim's  method  ;  if  from  the  frog,  the  cornea  can 
be  torn  with  fine  forceps  into  thin  lamellte,  which  are  mounted  whole. 
Sketch  three  or  four  of  the  connective-tissue  cells  (corneal  corpuscles)  The 
arrangement  and  distribution  of  the  nerve-fibres  and  their  termination 
amongst  the  epithelium-cells  as  shown  in  chloride  of  gold  preparations  have 
been  already  studied  (Lesson  XIX.,  p.  176). 

^The  celloidin  method  of  embedding  is  well  adapted  for  preparations  of  this 
kind. 


444  THE   ESSENTIALS  OF  HISTOLOGY. 

5.  Mount  in  dammar  sections  of  a  cornea  wliicli  has  been  stained  with 
nitrate  of  silver.  Notice  the  branched  cell-spaces  corresponding  with  the 
connective-tissue  cells  of  the  last  preparation. 

[This  preparation  is  best  made  by  rubbing  the  surface  of  the  cornea  of  a 
recently  killed  animal  with  lunar  caustic,  after  scraping  off  the  epithelium 
with  a  scalpel.  After  ten  minutes  (by  which  time  the  nitrate  of  silver  will 
have  penetrated  the  thickness  of  the  cornea)  the  eye  is  washed  with  distilled 
water,  and  exposed  to  the  light.  When  brown,  tangential  sections  may  be 
made,  for  which  purpose  the  stained  cornea  may  be  hardened  in  spirit.] 

6.  Eemove  the  sclerotic  from  the  anterior  part  of  an  eye  which  has  been 
preserved  in  Miillers  fluid,  and  tear  off  thin  shreds  from  the  surface  of  the 
choroid,  including  amongst  them  portions  of  the  ciliary  muscle.  Stain  the 
shreds  with  hsematoxylin  and  mount  them  in  glycerine.  Sketch  the  branched 
pigment-cells,  the  elastic  network,  the  mode  of  attachment  of  the  fibres  of 
the  ciliary  muscle,  etc. 

7.  Injected  preparation  of  choroid  and  iris.  Mount  portions  of  the  choroid 
coat  and  iris  from  an  eye  (preferably  of  an  albino  animal),  the  blood-vessels 
of  which  have  been  filled  with  coloured  injection.  Make  sketches  showing 
the  arrangement  of  the  capillaries  and  Aeins. 

8.  Teased  preparation  of  human  retina.  Break  up  with  needles  in  a  drop 
of  glycerine  a  minute  fragment  of  retina  which  has  been  placed  in  1  per 
cent,  osmic  acid  solution  for  some  hours,  and  has  subsequently  beeu  kept  in 
dilute  glycerine.  Complete  the  separation  of  the  retinal  elements  by  tapping 
the  cover-glass.  Draw  carefully  under  a  high  power  some  of  the  isolated 
elements — e.g.  the  rods  and  cones  with  their  attached  fibres  and  nuclei,  the 
inner  granules,  the  ganglion-cells,  the  fibres  of  Mliller,  hexagonal  pigment- 
cells,  etc.  In  some  of  the  fragments  the  arrangement  of  the  elements  in  the 
retinal  layers  may  be  made  oiit  even  better  than  in  actual  sections.^ 

Measure  the  length  and  diameter  of  some  of  the  cones,  the  length  of  the 
cone-fibres,  and  the  diameter  of  some  of  the  outer  and  inner  nuclei. 

9.  Teased  preparation  of  frog's  retina.  To  be  prepared  in  the  same  way  as 
8.  Notice  the  very  large  rods,  their  outer  segments  breaking  up  into  .disks, 
and  the  relatively  small  cones.  Also  the  pigment  extending  between  the 
rods,  the  distance  varying  according  as  the  eye  has  been  kept  in  the  dark  or 
in  the  light.     A  fresh  frog-retina  should  also  be  teased  in  salt  solution. 

10.  Sections' of  retina  of  ox  or  dog,  which  have  been  prepared  by  Golgi's 
method.  A  curled-up  piece  of  fresh  retina  is  placed  in  osmium-bichromate 
mixture  and  is  subsequently  treated  with  nitrate  of  silver  solution. - 

IL  Teased  preparation  of  lens.  Separate  in  Avater  the  fibres  of  a  crystalline 
lens  which  has  been  macerated  for  some  days  in  bichromate  of  potassium  or 
dilute  formol  solution.     Sketch  some  of  the  fibres,  together  and  separate. 


The  eyelids  (fig.  498)  are  covered  externally  by  the  skin,  and 
internally  or  posteriorly  by  a  mucous  membrane,  the  conjunctiva,  which 
is  reflected  from  over  the  globe  of  the  eye.  They  are  composed  in 
the  main  of  connective  tissue,  which  is  dense  and  fibrous  under  the 
conjunctiva,  where  it  forms  Avhat  is  known  as  the  tarsus. 

^  The  distribution  of  the  nerve-fibres  and  cell-processes  within  the  retina  can 
only  be  made  out  satisfactorily  by  the  employment  of  Golgi's  silver  chromate 
method  (see  §  10). 

^  See  Appendix.     Cajal's  reduced  silver  method  may  also  be  employed. 


THE   EYELIDS. 


445 


Embedded  in  the  tarsus  is  a  row  of  long  sebaceous  glands  (the 
Meibomian  glands,  /),  the  ducts  of  which  open  at  the  edge  of  the  eyelid. 
The  rest  of  the  thickness  of  the  eyelid  is  composed  of  a  somewhat 
loose   connective   tissue,   and  contains  the  bundles  of  the  orbicularis 


Fig,  498. — Vertical    sectiox    through   the   upper   eyelid. 


(Waldejer. ) 


a,  skin  ;  i,  orbicularis ;  h' ,  ciliary  bundle ;  c,  involuntary  muscle  of  eyelid  ;  d,  con- 
junctiva ;  (',  tarsus  vfitli  Meibomian  gland  ;  f,  duct  of  the  gland  ;  <i,  sebaceous  gland 
near  eyelashes  ;  A,  eyelashes ;  (',  small  hairs  in  outer  skin ;  j,  sweat-glands  ;  k,  pos- 
terior tarsal  glands. 


muscle  ih).  In  the  ui)per  eyelid  the  levator  palpebne  is  inserted  into 
the  tarsus  by  a  fibrous  expansion,  and  some  bundles  of  involuntary 
muscle  are  also  present  near  the  attachment  of  the  eyelid.  The  skin 
has  the  usual  structure ;  it  contains  small  sweat-glands,  and  the 
follicles  of  small  hairs,  and,  in  addition,  at  the  edge  of  the  eyelid,  the 


446 


THE   ESSENTIALS  OF  HISTOLOGY. 


large  hair-follicles  from  which  the  eyelashes  grow.  The  epithelium 
of  the  conjunctiva  palpebrse  is  columnar,  passing  at  the  edge  of  the 
lid  into  the  stratified  epithelium  of  the  skin  ;  it  also  becomes  stratified 
in  the  part  which  is  reflected  over  the  globe  of  the  eye.  The  nerves  of 
the  conjunctiva  terminate  for  the  most  part  in  end-bulbs,  which  in  man 
are  spheroidal,  and  formed  chiefly  of  a  small  mass  of  polyhedral  cells ; 
but  in  the  calf  and  most  animals  they  are  elliptical. 

The  lacrymal  gland  may  be  briefly  mentioned  in  connection  with 
the  eyelid.  It  is  a  compound  racemose  gland,  yielding  a  watery 
secretion.     Its  alveoli  are  lined  by  columnar  cells,  which  are  normally 


^io 


,^ 


Fig.  499. — Section  of  l.4Crtjial  gland  of  dog.    A,  resting  ;   B,  after 

COPIOUS    SECRETION    PRODUCED    BY    PILOCARPINE. 


filled  with  granules,  but,  after  profuse  secretion,  these  disappear,  and 
the  cells  become  much  shorter  and  smaller  (fig.  499,  A,  B).  Its  ducts,, 
of  which  there  are  several,  open  at  the  upper  fold  of  the  conjunctiva, 
near  its  outer  extremity. 

The  globe  of  the  eye  (fig.  500)  is  inclosed  by  three  coats,  the  cornea- 
sclerotic,  choroid  (with  the  iris),  and  retina.  It  is  filled  by  the 
vitreous  and  aqueous  humours  and  the  crystalline  lens  which  lies 
between  them. 

The  sclerotic  coat  is  composed  of  dense  fibrous  tissue,  the  bundles 
of  which  are  intimately  interlaced.  It  is  thickest  at  the  back  of  the 
eyeball.  It  is  covered  externally  with  a  lymphatic  endothelium,  while 
internally  it  is  lined  by  a  layer  of  connective  tissue  containing  pigment- 
cells,  which  give  it  a  brown  appearance  (luinina  fusca).     At  the  entrance- 


THE  CORNEA. 


447 


of  the  optic  nerve  the  sclerotic  is  prolonged  into  the  sheath  of  that 
nerve,  the  bundles  of  which,  piercing  the  coat,  give  a  sieve-like  aspect 
to  the  part  {hniiina  crihrosa,  tig.  512,  L.). 


CANAL   OF   SCHLEMM 


SCLEROTIC 


CENTRAL  ARTERY  OF  RETINA  


optic  nerve 
Fig.  .500.— Diagram  of  a  section  through  the  (right)  human  eye  passing 

HORIZONTALLY      NEARLY      THROUGH      THE      MIDDLE.         (Magnified      about      4 

diameters.) 

a,  h,  equator ;  ,/■,  y,  optic  axis. 

The  cornea  (fig.  501)  consists  of  the  following  layers  (enumerated 
from  before  back) : 

1.  A   stratified   epithelium   continuous    with    the    epithelium    of  the 
conjunctiva  (1 ). 

2.  A  thin  lamina  of  homogeneous   connective  tissue   {membrane   of 
Bowman),  upon  which  the  deepest  cells  of  the  epithelium  rest  (2). 


448 


THE   ESSENTIALS   OF  HISTOLOGY. 


3.  A  thick  layer  of  fibrous  connective  tissue  which  forms  the  pr<yper 
substance  of  the  cornea  (3).     This  is  continuous  laterally  with  the  tissue 


Fig.  501. — Veetical  sectiox  of  hcmax  corxea  fbom  xear  the  margin. 

(Waldeyer. )  (Magnified.) 
1,  epithelium ;  2,  anterior  homogeneous  lamina  ;  3,  substantia  propria  comese  ;  4,  pos- 
terior homogeneous  (elastic)  lamina ;  5,  epithelium  of  the  anterior  chamber ;  a,  oblique 
fibres  in  the  anterior  layer  of  the  substantia  propria  ;  h,  lamellae,  with  their  fibres 
cut  across,  producing  a  dotted  ajjpearance  ;  c,  corneal  corpuscles  appearing  fu-siform 
in  section ;  d,  lamellae  with  the  fibres  cut  longitudinally  ;  e,  transition  to  the 
sclerotic,  with  more  distinct  fibrillation,  and  surmounted  by  a  thicker  epithelium  ; 
/,  small  iilood-vessels  cut  across  near  the  margin  of  the  cornea. 

of  the  sclerotic.  It  is  composed  of  bundles  of  white  fibres  arranged 
in  regular  laminae,  the  direction  of  the  fibres  crossing  one  another  at 
right  angles  in  the  alternate  laminae.    Between  the  laminae  lie  flattened 


THE   CORNEA. 


449 


connective-tissue  corpuscles  (fig.  502),  which  are  branched  and  united 
by  their  processes  into  a  continuous  network ;  there  is  of  course  a 
corresponding  network  of  cell-spaces.  In  vertical  sections  the  cells 
appear  narrow  and  spindle-shaped  (fig.  501,  c).  In  the  superficial 
lamina  there  are  a  few  bundles  of  fibres  which  run  obliquely  towards 
the  surface  (a). 

4.  A  homogeneous  elastic  layer  {membrane  of  Descemet,  fig.  501,  4). 
This  completely  covers  the  back  of  the  cornea,  but  near  the  angle 
which  the  cornea  forms  with  the  iris  it  breaks  up  into  separate  fibres 
{ligamentum  pedinatum)  which  are  partly  continued  into  the  iris  as 
the  pillars  of  the  iris. 


Fig.  .502. — Corpuscles  of  the  cornea,  isolated.     (Waldeyer.) 


5.  A  layer  of  pavement-epithelium  {epithelium  of  Descemefs  membrane) 
covering  the  posterior  surface  of  the  elastic  lamina,  and  lining  the 
front  of  the  anterior  chamber  of  the  eye  (fig.  501,  5).  At  the  sides 
it  is  continued  over  the  ligamentum  pectinatum  into  a  similar  epithe- 
lium, covering  the  anterior  surface  of  the  iris.  The  cells  of  the 
epithelium  of  Descemets  membrane  are  separated  from  one  another 
by  intercellular  spaces,  bridged  across  by  bundles  of  fibrils  which  pass 
through  the  cells  (fig.  503).  Each  cell  has  a  peculiar  basket-like 
reticulum  close  to  the  nucleus  :  perhaps  a  modified  centrosome. 

The  nerves  of  the  cornea  pass  in  from  the  periphery,  losing  their 
medullary  sheath  as  they  enter  the  corneal  substance.  They  form 
a  primary  plexus  in  the  substantia  propria,  a  secondary  or  sub 
epithelial  plexus  immediately  under  the  epithelium  which  covers  the 
anterior  surface,  and  a  terminal  plexus  of  fine  fibrils  which  pass 
from   the   subepithelial   plexus  in  pencil-like   tufts  and   become   lost 

2f 


450 


THE   ESSENTIALS   OF  HISTOLOGY 


between  the  epithelium-cells   (Fig.  504-).     There  are  no  blood-vessels 
or  lymphatics  in  the  cornea,  although  they  come  close  up  to  its  margin. 


/l\m 


M 


Fig.   503. — Epithelium-cells   of   descemet's    membrane.      (After    Sinirnow 

and  Nutjl.) 


— ^— .  h 


i^^iljii. 


•SfSe-r 


Fig.  504. — Vertical  sectiox  through  the  cornea.     (Barker,  after  Cohnheim.) 

The  corneal  corpuscles  and  the  cells  of  Descemet's  membrane  are  not  represented  ;  the 
anterior  epithelium  has  been  drawn  in  only  in  part,  n,  Descemet's  membrane  ;  6, 
parts  of  nerve  plexus  in  substantia  propria  ;  c,  branches  going  to  the  epithelium  ;  rf, 
fibres  of  the  subepithelial  Layer;    e,   vertical  fibrils  with  horizontal  outrunners. 


THE   CHOROID   COAT. 


451 


The  choroid  or  vascular  coat  of  the  eye  is  of  a  black  colour  in 
many  animals,  hut  in  the  human  eye  it  is  dark  hrovvn.  It  is  com- 
posed of  connective  tissue,  the  cells  of  which  are  large  and  filled 
with  pigment  (tigs.  505,  506).     It  contains  in  its  inner  layer  a  close 


CAOIAT.a£,. 


Fig.  50.5. — Section  of  choroid.     (Cadiat. ) 

a,  membrane  of  Bruch  :  the  chorio-capillaris  is  just  above  it ;  b,  vascular  layer ;  c,  vessels 

with  blood-corpuscles  ;  (/,  lamina  suprachoroidea. 


Fig.   506. — A  small  portion    of  the    lamina    suprachoroidea.     (Highly 

magnified.) 

The  pigment-cells  and  elastic  fibres  are  well  shown  ;   n,  nuclei  of  endothelial  cells  (the 

outlines  of  the  cells  are  not  indicated) ;  I,  lymph-cells. 

network  of  blood-vessels,  and  in  its  anterior  part  the  involuntary 
muscular  fibres  of  the  ciliary  muscle,  which  pass  backwards  from 
their  origin  at  the  junction  of  the  cornea  and  sclerotic,  to  be  inserted 
into  the  choroid.  The  choroid  is  separable  into  the  following  layers 
(enumerated  from  without  in): 

1.  The  lamina  suprachoroidea  (fig.  505,  (/).     This  is  a  loose  membrane 


452 


THE   ESSENTIALS  OF   HISTOLOGY. 


composed  of  delicate  connective  tissue  pervaded  by  a  network  of  fine 
elastic  fibres,  and  containing  many  large  branched  pigment-cells  and 
lymph-corpuscles  (fig.  506).  It  is  covered  superficially  by  a  lymphatic 
endothelium,  and  is  separated  from  the  lamina  fusca  of  the  sclerotic 
by  a  cleft-like  lymph-space  which  is  bridged  across  here  and  there  by 
the  passage  of  vessels  and  nerves,  and  by  bands  of  connective  tissue. 

2.  The  vascular  layer  of  the  choroid  (fig.  505,  h),  which  resembles 
the  suprachoroidea  in  structure,  l)ut  contains  the  blood-vessels  of  the 


Fig.  507. — Injected  blooij-ve.ssels  of  the  choroid  coat.     (Sappey.) 
1,  one  of  the  larger  veins;  2,  small  anastomosing  vessels  ;  3,  branches  dividing  into  the 

smallest  vessels. 


coat.  In  its  outer  part  are  the  larger  vessels  (arteries  and  veins), 
the  veins  having  a  peculiar  vorticose  arrangement;  in  its  inner  part 
(chorio-capillaris)  are  the  capillaries,  Avhich  form  an  extremely  close 
network  with  elongated  meshes,  the  capillaries  radiating  from  the 
extremities  of  the  small  arteries  and  veins  in  a  highly  characteristic 
maimer  (fig.  507).  In  the  ciliary  processes  the  vessels  have  for  the 
most  part  a  longitudinal  direction,  but  there  are  numerous  convo- 
luted transversely  disposed  capillaries  uniting  the  longitudinal  vessels 
(fig.  510,  d). 

3.  Lining  the  inner  surface  of  the  choroid  is  a  thin  transparent 
membrane  known  as  the  memhrane  of  Bruch  (fig.  505,  a). 

The  ciliary  muscle  consists  of  involuntary  muscular  bundles  which 
arise  at  the  corneo-sclerotic  junction,  and  pass  meridionally  backwards 


THE  IRIS. 


453 


to  1)0  inserted  in  the  choroid  (fig.  TiOS,  ilf).  Many  of  the  deeper- 
seated  bundles  take  an  o])li(iue  direction,  and  these  pass  gradually  into 
others  which  run  circularly  around  the  circumference  of  the  iris,  and 
on  a  level  with  the  ciliary  processes.  This  set  of  circularly  arranged 
l)undles  constitutes  the  cirmlar  ciliary  muscle  of  H.  Miiller  (Mu.) ;  it  is 
most  marked  in  hypermetropic  eyes. 


Fig.  50.S.— Section  through  the  ciliary  part  of  the  eye,  including  part 
OF  the  cornea,  the  ora  serrata,  the  iris  and  the  edge  of  the  lens 

WITH  its  suspensory  LIGAMENT.  (Fuchs.) 
C,  cornea  ;  S,  sclerotic  ;  Ch,  choroid  ;  B,  retina  ;  Fc,  its  pigmented  epithelium  ;  0,  pars 
ciliaiis  :  this  is  continued  over  the  choroid  processes;  p.(.,  p.c,  pigmented  and 
non-pigmented  layer  of  par.s  ciliaris ;  L,  lens  ;  3f,  ciliary  muscle  ;  /•,  its  radiatinsj 
(meridional)  fibres  passing  from  their  origin  at  the  corneo-sclerotic  junctiou  ;  ilu, 
circular  ciliary  muscle;  ci,  artery  of  sclerotic  ;  s,  vein  (canal  of  Schlemm) ;  :,  fibres 
of  zonula  of  Zinn  pas^sing  between  choroid  jirocesses  into  the  suspensorj-  ligament 
of  the  lens  (;',  ;)  I  'i  augle  of  anterior  chamber;  sp,  sphincter  pupillas;  p,  edge  of 
pupil;  A,  pigmented  epithelium  of  iris  (accidentally  detached  at  this  point);  c,  c,f,  /", 
creases  and  folds  of  anterior  surface  of  iris  ;  cr,  a  fissure  in  this  surface  (accidental) ; 
a,  artery  at  insertion  of  iris  ;  k-,  capsule  of  lens. 

The  iris  is  that  part  of  the  vascular  coat  of  the  eye  which  extends 
in  front  of  the  lens.  It  is  continuous  with  the  choroid  and  has  a 
similar  structure,  but  its  pigment-cells  often  contain  variously  coloured 
pigment.  Besides  the  delicate  connective  tissue  with  numerous 
elastic  fibres  and  blood-vessels  of  which  it  is  chiefly  composed,  it 
contains  two  sets  of  plain  muscular  fibres.  The-  one  set  forms  the 
sphincter  muscle  (figs.  508,  sjj.,  509,  a),  which  encircles  the  pupil;  the 
other    set    consists   of    a    flattened    layer   of    radiating   fibres   which 


454 


THE   ESSENTIALS   OF   HISTOLOGY. 


extend  from  the  attachment  of  the  iris  nearly  to  the  pupil,  lying 
close  to  the  posterior  surface  and  constituting  the  dilatator  muscle 
(fig.  509,  h). 

The  back  of  the  iris  is  covered  by  a  thick  layer  of  pigmented 
epithelium  (uvea)  continuous  with  the  epithelium  of  the  pars  ciliaris 
retinae. 

The  muscular  tissue  of  the  iris  is  stated  to  be  developed  from  the  epithelium 
at  the  back  of  the  iris  (Nussbauni,  Szili). 


Fig.  509. 

Fig.  509. — Segment  op  the  iris,  seen  from  the  pos- 
terior    SURFACE     after     REMOVAL     OF     THE     UVEAL 
PIGMENT.     (Iwanoff.) 
a,  sphincter  muscle  ;  6,  dilatator  muscle  of  the  pupil. 


Fig.  510.-  Vessels  of  the  choroid,  ciliary  processes 
AND  IRIS  of  a  child.     (Arnold.)     (10  diameters.) 

a,  capillary  network  of  the  posterior  part  of  the  choioid,  ending 
at  b,  the  ora  serrata ;  c,  arteries  of  the  corona  ciliaris.  supjilying 
the  ciliary  processes,  d,  and  passing  into  the  iris,  <■ ;  /,  the 
capillary  network  close  to  the  papillary  margin  of  the  iris. 


Fig.  510. 


The  blood-vessels  of  the  iris  (fig.  510,  e)  converge  towards  the  pupil. 
Near  the  pupil  the  small  arteries  form  an  anastomotic  circle,  from 
which  capillaries  arise  and  pass  still  nearer  the  pnpil,  around  which 
they  form  a  close  capillary  network. 

A  large  number  of  nerve-fibres  are  distributed  to  the  choroid  and 
iris,  probably  going  chiefly  to  the  muscular  tissue  of  those  parts  (ciliary 
muscle  and  sphincter  and  dilatator  pupillse). 

The  retina  consists  of  the  eight  layers  shown  in  the  accompanying 
figure  (fig.  511),  numbered  as  they  occur  from  within  out. 

The  inner  surface  of  the  retina,  which  is  smooth,  rests  upon  the 
hyaloid  membrane  of  the  vitreous  humour.  It  is  formed  of  the  united 
bases  of  the  fibres  of  Midler,  which  will  be  afterwards  described. 

The  layer  of  nerve-fibres  is  formed  by  the  expansion  of  the  optic  nerve 
after  it  has  passed  through  the  coats  of  the  eye  (fig.  512).     At  its 


THE   EETINA. 


465 


entrance  the  nerve  forms  a  sliii;lit  eminence  {roUiculus  nervi  cptici).  The 
nerve-fibres  lose  their  medullary  sheath  on  reaching  the  retina.  Most 
are  connected  with  (derived  from)  the  cells  of  the  ganglionic  or  optic 
nerve-cell  layer  (fig.  513),  but  some  (centrifugal)  fibres  pass  through 
the  ganglionic  and  molecular  layers  to  form  a  terminal  arborisation  in 


S.  Layer  of  pigment-cells. 


7.  Laver  of  rods  and  cones. 


Membrana  limitans  externa. 


6.  Outer  nuclear  layer. 


0   Outer  synapse  or  molecular  layer. 


4.  Inner  nuclear  or  bipolar  layer. 


3.  Inner  synapse  or  molecular  layer. 


•2.  Layer  of  optic  nerve-cells. 

1 .  Layer  of  optic  nerve-fibres. 

.     .     .     Membrana  limitans  interna. 

inner  burtLuw 

Fig.  511. — Diagrammatic  section*  of  the  human  retina.     (M.  Schultze.) 

the  inner  nuclear  layer  (fig.  51-4  and  fig.  513,  j).     The  layer  of  nerve- 
fibres  becomes  gradually  thinner  in  the  anterior  part  of  the  retina. 

The  lai/er  of  optic  n-erve-cells,  or  ganglionic  layer,  is  composed  of  nerve 
cells  somewhat  like  the  cells  of  Purkinje  of  the  cerebellum  but  varying 
in  size,  although  those  of  large  size  are  prevalent  in  most  parts  of  the 
retina.  In  the  j-ellow  spot,  on  the  other  hand,  smaller  nerve-cells  are 
met  with,  and  they  may  here  lie  several  deep.     These  nerve-cells  have 


THE   ESSENTIALS  OF  HISTOLOGY. 


-1        .0 


Fig.  512.— Section  thuocgh  the  coat.s  of  the  eyeball  at  the  point  of 

ENTRANCE  OF  THE  OPTIC  NERVE.  (Tolilt.) 
Ve,  dural  sheath  ;  Vm,  araclmoidal  sheath,  and  17,  pia-matral  sheath  of  the  optic  nerve, 
with  lymphatic  spaces  between  them;  0,  0..  funiculi  of  the  nerve  ;  L,  lamina  cribrosa; 
A,  central  artery  ;  S,  sclerotic  ;  CA,  choroid  ;  R,  retina.  The  small  letters  refer  to  the 
various  parts  of  the  retina,  h  being  the  layer  of  rods  and  cones,  and  i  that  of  nerve- 
fibres. 


Fig.  .513. — Section  of  dog's  retina,  golgi  method.  (Cajal.) 
<t,  cone-fibre ;  h.  rod-fibre  and  nucleus  ;  c,  i/,  bipolar  cells  (inner  gi-anides)  with  vertical 
ramifications  of  their  outer  processes  or  dendrons :  in  the  centie  of  the  ramific.ition 
lie  the  enlarged  ends  of  rod-fibres ;  t,  other  bipolars  with  flattened  ramifications 
abutting  against  ramified  ends  of  cone-fibres  ;  /,  large  bipolar  with  flattened  ramifica- 
tion ;  tj,  inner  granvile-cell  sending  an  axon  towards  the  rod  and  cone-fibres ;  A, 
amacrine  cell  with  di£fu.«e  arborisation  of  its  processes  in  inner  molecular  layer; 
i,  j,  III,  nerve-fibrils  passing  respectively  to  outer  molecular,  inner  nuclear,  and  inner 
molecular  layers  ;  »>,  ganglionic  cells,  with  axons  passing  into  nerve-fibre  layer. 


THE   RETINA. 


457 


a  fino  axis-cylinder  process  proloiii^ed  into  a  fil)re  of  the  layer  just 
noticed,  and  a  thick  branching  process,  the  ramifications  of  which 
terminate  in  the  next  layer  in  flattened  arborisations  at  different  levels 
(fig.  015,  A,  B,  C). 

The  inner  si/n(q)f<e  layer  or  inner  molecular  layer  is  comparatively  thick, 
and  has  an  appearance  very  like  parts  of  the  grey  matter  of  the  nerve- 


FiG.  514. — Section  through  the  innek  layers  op  the  retina  of  a  bird, 

PREPARED    BY   GOLGl's   METHOD.       (Cajal. ) 
A,  nerve-fibres  of  optic  nerve  la}'cr  ;  B,  some  of  these  fibres  passing  through  the  inner 
molecuhir  layer  to  end  in  an  arborisation  at  the  junction  of  the  inner  molecular 
and  inner  nuclear  layers.     The  layers  in  this  and  in  the  two  succeeding  cuts  are 
numbered  in  correspondence  with  the  layers  in  fig.  511. 


centres.  A  few  nuclei  are  scattered  through  it,  and  it  is  occupied  by 
the  processes  of  the  nerve-cells  and  of  the  inner  granules  (bipolars  and 
amacrine  cells)  which  form  synapses  in  it ;  it  is  also  traversed  by  the 
centrifugal  fibres  from  the  optic  nerve  layer,  as  well  as  by  the  fibres  of 
Muller. 


Fig.  515.  — Section  across  the  molecular  and  ganglionic  layers  of  bird's 

RETINA,    prepared   BY   GOLGl'S   METHOD.      (Cajal.) 

Three  or  four  ganglionic  cells,  A,  B,  C,  and  the  terminal  arborisations  of  their  dendrons, 

(«,  b,  c,  in  the  molecular  layer,  are  shown. 

The  inner  gramde  layer  (also  termed  inner  nuclear  layer)  is  mainly 
composed  of  bipolar  nerve-cells  containing  large  nuclei.  A  process 
(the  axon)  of  each  of  these  cells  (fig.  513)  extends  inwards  into  the 
inner  molecular  layer  where  it  spreads  out  into  a  terminal  arbori- 
sation. These  arborisations  occur  at  different  levels  in  the  layer, 
forming  synapses  with  the  optic  nerve-cells.  Another  process 
(dendron)  is  directed  outwards,  and  arborises  in  the  outer  molecular 


458 


THE   ESSENTIALS   OF  HISTOLOGY. 


layer,  where  it  forms  synapses  with  the  terminations  of  the  rod-  and 
cone-fibres.  It  has  been  shown  by  Ram6n  y  Cajal  that  there  are  two 
kinds  of  bipolars,  one  kind  (rod-hipolars,  fig.  513,  c.d)  being  connected 
externally  with  the  rods  of  the  retina,  and  passing  inwards  to  ramify 
over  the  bodies  of  the  nerve-cells,  whereas  those  of  the  other  kind 
{cone-hipolars,  e)  are  connected  with  the  cone-fibres,  and  ramify  in  the 
middle  of  the  inner  molecular  layer.  The  outwardly  directed  pro- 
cesses of  these  cone-bipolars  are,  in  some  animals,  but  not  in  mammals, 


liilliliMiiiiin 


Fig.  5L6.— Section  of  bird's  retina,  prepared  by  golgi's  method. 
(Cajal.) 
A,  large  nerve-cell  of  inner  nuclear  layer ;  B,  C,  amacrine  cells  ;  D,  small  bipolar  nerve- 
cells  with  one  process,  ramifying  in  the  inner  molecular  layer  and  the  other  one 
ramifying  in  the  outer  molecular  layer,  and  extending  (E)  as  far  as  the  rods  and 
cones  as  a  fibre  of  Laudolt ;  F,  G,  rod-  and  cone-nuclei  respectively;  H,  I,  cells  with 
dendrons  ramifying  in  outer  molecular  layer  ;  J,  fibre  of  Miiller. 

continued  on  as  far  as  the  external  limiting  membrane,  where  each 
ends  in  a  free  extremity  {fibre  of  Landolt,  fig.  516,  E).  Besides  these 
bipolar  nerve-cells,  there  are  other  larger  inner  granules  (spongioblasts 
of  some  authors)  which  are  different  in  character,  having  ramified 
processes  which  extend  into  the  inner  molecular  layer  (figs.  513,  h ; 
516,  A,  B,  c),  in  which  the  bodies  of  these  cells  are  often  partly 
embedded.  The  cells  in  question  have  been  regarded  as  of  the  nature 
of  neuroglia-cells,  but  according  to  Cajal  they  are  probably  all  nerve- 
cells.  He  has  termed  them  amacrine-cells,  from  the  fact  that  they  are 
destitute  of  a  long  process  ;  but  some  have  been  noticed  to  give  off, 
besides  the  branching  processes  or  dendrons,  which  ramify  in  the 
molecular  layer,  an  axis-cylinder  process  which  may  extend  into  the 


THE   RETINA. 


459 


nerve-fibre  layer.  There  are  also  some  cells  in  the  outer  part  of  the 
granule  layer  which  send  their  processes  entirely  into  the  outer  molecular 
layer  (fig.  516,  h).  These  are  the  horizontal-cells  of  Kam6n  y  Cajal 
(termed  spongioblasts  of  outer  molecular  layer  by  some  authors). 
The  fibres  of  Miiller  have  nucleated  enlargements  (fig.  516,  .i)  in  the 
inner  nuclear  layer. 

The  Older  molecular  lai/er  is  thin,  and  is  composed  mainly  of  the 
arborisations  of  the  inner  granules,  of  the  rod  and  coae-fibres,  and  of 
the  horizontal  cells  (figs.  513,  516), 
which  all  form  synapses  in  this  layer. 

The  Older  nuclear  layer  and  the  lat/er 
of  rods  and  cones  are  composed  of 
elements  which  are  continuous  through 
the  two  layers,  and  they  should  pro- 
perly, therefore,  be  described  as  one. 
It  has  been  termed  the  sensory  epi- 
thelium of  the  retina  (fig.  517,  6  and  7). 
The  elements  of  which  this  nerve- 
epithelium  consists  are  elongated 
nerve-cells  of  two  kinds.  The  most 
numerous,  which  may  be  termed  the 
rod-elements,  consist  of  peculiar  rod-like 
structures  {retinal  rods)  set  closely  side 
by  side,  each  of  which  is  prolonged 
internally  into  a  fine  varicose  fibre 
{rod-fibre)  Avhich  swells  out  at  one  part 
of  its  course  into  a  nucleated  enlarge- 
ment, and  ultimately  ends  (in  mam- 
mals) in  a  minute  knob  within  the 
outer  molecular  layer,  where  it  is  em- 
bedded in  the  ramifications  of  the  dendrons  of  the  rod-bipolars. 
The  rod  consists  of  two  segments,  an  outer  cylindrical  and  trans- 
versely striated  segment,  which  during  life  has  a  purplish-red  colour 
if  the  eye  has  not  been  recently  exposed  to  light,  and  an  inner 
slightly  bulged  segment  which  in  part  of  its  length  is  longitudinally 
striated.  The  nucleus  of  the  rod-element  in  some  animals,  but  accord- 
ing to  Flemming  not  in  man,  has  a  transversely  shaded  aspect  in  the 
fresh  condition  (fig.  517).  The  cone-elements  are  formed  of  a  conical 
tapering  external  part,  the  retinal  cone,  which  is  directly  prolonged 
into  a  nucleated  enlargement,  from  the  farther  side  of  which  the 
cone-fibre,  considerably  thicker  (in  mammals)  than  the  rod-fibre,  passes 
inwards,  to  terminate  by  an  expanded  arborisation  in  the  outer  mole- 


FiG.    .517.  —  Diagrammatic    repre- 

SEXTATION  OF  THE   ROD  AND   CONE 
ELEMENTS  OF  THE  RETINA.       (After 

Schwalbe. ) 
The  designation  of  the  numbers  is  the 
same  as  in  fiff.  oil. 


460 


THE   ESSENTIALS   OF   HISTOLOGY. 


cular  layer ;  here  it  comes  into  relation  Avith  a  similar  arborisation 
of  dendrons  of  a  cone-bipolar.  The  cone,  like  the  rod,  is  formed  of 
two  segments,  the  outer  of  which,  much  the  smaller,  is  transversely 
striated  ;    the   inner,    bulged   segment   being   longitudinally  striated. 


Fig.  .'i19.— PiGMENTEn  epithelium  of  the 
HUMAN  RETINA.  (M.  Schultze.)  (Highly 
magnified.) 

a,  cells  seen  from  the  outer  surface  with  clear 
lines  of  intercellular  substance  between ;  0, 
two  cells  seen  in  profile  with  fine  offsets 
extending  inwards ;  c,  a  cell  still  in  connection 
with  the  outer  ends  of  the  rods. 


'Sr^ 


Fig. 


518. — Diagram  of  the  connections  of  the  retinal  elements  with 

ONE    another    and    WITH    THE    CENTRAL    NERVOUS    SYSTEM.        (Cajal.) 

o  to  g,  layers  of  retina ;  a,  rods  and  cones ;  6,  outer  nuclear  layer ;  c,  outer  molecular 
layer  ;  U,  inner  nuclear  layer  ;  i,  inner  molecular  layer ;  /,  nerve-cells  giving  origin  to 
fibres  of  optic  nerve  ;  p,  h,  i,  a  centrifugally  conducting  fibre,  with  a  terminal 
arborescence  in  the  retina ;  j,  grey  matter  of  corpus  geniculatum  or  corpus  quadri- 
geminum. 

The  inner  ends  of  the  rod-  and  cone-fibres,  as  already  stated,  form 
synapses  with  the  peripheral  arborisations  of  the  bipolars,  and  through 
the  latter  elements  and  their  sjmapses  in  the  inner  molecular  layer 
a  connection  is  brought  about  with  the  nerve-cells  and  nerve-fibres  of 
the  innermost  layers.  The  connection  of  the  retinal  elements  with 
one  another  and  through  the  optic  fibres   with   the  central  nervous 


THE   RETINA. 


461 


system  (aiiterior  corpora  (luadrigeiniiia  and  lateral  geniculate  l)O(lies) 
is  shown  diagrammatically  in  fig.  518. 

In  birds,  reptiles,  and  amphibia,  a  small  oil-globule,  often  lirightly 
coloured  red,  yellow,  or  green,  is  found  in  the  inner  segment  of  each 
cone.     Other  variations  of  structure  are  met  with  in  different  animals. 

The  cones  are  most  numerous  at  the  back  of  the  retina ;  they  are 
fewer  in  number,  and  the  rods  are  proportionally  more  numerous 
towards  the  anterior  part. 


J 


pff 

^'^ 

^tV*^ 

pi  yi<a->i^ 

1 

'■^HH 

Fig.  520. — A.  Part  of  a  section  of  the  retina  feoji  the  eye  of  a  fkog 

WHICH    HAD    BEEN    KEPT    IN    THE    DARK    FOR    SOME    HOURS    BEFORE    DEATH. 

(v.  Genderen-Stort. ) 
The  pigment  is  collected  towards  the  outer  ends  of  the  rods,  which  were  red,  except  the 
outer  detached  rod,  which  was  green.      The  cones,  which  in  the  frog  are  much 
smaller  than  the  rods,  are  mostly  elongated. 

B.     A   SIMILAR   SECTION    FROM    A   FROG    WHICH    HAD    BEEN    EXPOSED    TO   LIGHT. 

The  pigment  is  extended  between  the  rods,  and  is  accumulated  near  their  bases.     The 

rods  were  colourless.     All  the  cones  are  contracted. 

The  pigmentary  layer  forms  the  most  external  part  of  the  retina.  It 
consists  of  hexagonal  epithelium-cells  (fig.  519),  which  are  smooth 
externally  where  they  rest  against  the  choroid,  but  are  prolonged 
internally  into  fine  filaments  which  extend  between  the  rods.  The 
pigment-granules,  many  of  which  are  in  the  form  of  minute  crystals, 
lie  in  the  inner  part  of  the  cell,  and  after  prolonged  exposure  to  light 
they  are  found  extending  along  the  cell-processes  between  the  rods 
(Kiihne),  their  function  being  probably  connected  with  the  restoration 
of  the  purple  colouring  matter  which  has  been  bleached  by  the  light. 
This  extension  of  the  pigment  is  accompanied  by  a  shortening  of  the 
cones  (Engelmann)  (fig.  520). 


462 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fibres  of  31uller.— The  fibres  of  Miiller  (fig.  516,  /,  and  fig.  521)  are 
long  stiff  cells  which  pass  through  several  of  the  retinal  layers. 
Commencing  at  the  inner  surface  of  the  retina  by  expanded  bases 
which  unite  with  one  another  to  form  the  so-called  internal  limiting- 
membrane  (fig.  522),  they  pass  through  all  the  layers  in  succession, 
until   they    reach    the    outer   granule  layer.     Here  they   branch  and 


m.l.e. 


m.l.i. 


Fig.  .521. 


KiG.  522. 
Fig.   521. — A  fibre  of  mullek  from  the   dog's 

RETINA,  GOLGI  METHOD.  (Cajal.) 
1,  nerve-fibre  layer  ;  2,  nerve-cell  layer  ;  3,  inner  molecular 
layer  ;  4,  inner  ftranule  lajer  ;  5,  outer  molecular  layer;  6, 
outer  granule  layer  ;  b,  nucleus  of  the  fibre  ;  a,  a  process 
extending  into  inner  molecular  layer  ;  m.l.i,,  membrana 
limitans  interna ;  m.l.e.,  membrana  limitans  externa. 


Fig.  522. — Intern.\l  lijiiting  membrane  of  retina 
treated  with  silver  nitrate,  showing  the  out- 
lines of  the  b^\ses  of  the  fibres  of  muller. 
(G.  Retzius. ) 


expand  into  a  sort  of  honeycomb  tissue  which  serves  to  support  the 
fibres  and  nuclei  of  the  rod-  and  cone-elements.  At  the  bases  of  the 
rods  and  cones,  this  sustentacular  ti.ssue  ceases,  being  here  bounded  by 
a  distinct  margin  which  has  been  called  the  external  limiting  membrane 
(fig.  521,  m.l.e.),  but  delicate  sheaths  pass  from  it  around  the  bases  of 
the  rods  and  cones.  Each  Miillerian  fibre,  as  it  passes  through  the 
inner  granule  layer,  has  a  nucleated  enlargement  (b),  indicating  the 
cell-nature    of  the  fibre.     The  fibres  of  Miiller  represent   ependyma 


THE   RETINA. 


463 


cells  or  perhaps  long  neuroglia-cells  such  as  are  found  in  some  parts 
of  the  nerve-centres,  e.g.  the  cerebellum  (see  fig.  479,  (jl^). 

There  are  two  parts  of  the  retina  which  call  for  special  description. 

The  macula  lutea  (yellow  spot),  with  its  central  fovea,  is  the  part 
of  the  retina  which  is  immediately  concerned  in  direct  vision.  It  is 
characterised  firstly  by  its  greater  thickness  (except  at  the  middle  of 
the  fovea),  secondly  by  the  large  number  of  its  ganglion-cells,  which 
are  rounded   or  conical,  and  thirdly  by   the  large  number   of  cones 


Fig.  523. — Section  through  the  central  part  of  the  fovea  centralis. 
''f-^.     (From  a  preparation  by  C.  H.  Golding-Bird.) 

M,  bases  of  Miillerian  fibres;   c.h.,  nuclei  of  inner  granules  (bipolars) ;   c.n.,  cone-fibre 

nuclei ;   c,  cones. 

it  contains  as  compared  with  the  rods.  In  the  central  fovea  itself 
(fig.  523)  there  are  no  rods,  and  the  cones  are  very  long  and 
slender,  measuring  not  more  than  2/^  in  diameter ;  all  the  other  layers 
become  gradually  thinned  down  almost  to  complete  disappearance,  so 
that  the  middle  of  the  central  fovea  is  the  thinnest  part  of  the  retina. 
Since  there  are  fcAv  rods,  the  outer  granule  layer  loses  in  great 
measure  its  appearance  of  being  composed  of  closely  packed  nuclei, 
and  the  cone-fibres  are  very  distinct,  forming  the  so-called  fihrous  layer. 
The  direction  of  these  fibres  is  for  the  most  part  very  oblique  in  this 
part  of  the  retina. 


464 


THE   ESSENTIALS   OF   HISTOLOGY. 


Fig.  525. — Section  through  the  mar- 
gin OF  THE  babbit's  LENS,  SHOWING 
THE  TRANSITION  OF  THE  EPITHELIUM 
OP  THE  CAPSULE  INTO  THE  LENS- 
FIBRES.     (Babuchin.) 


Fig.  524. — A  small  portion  of  the  ciliary 
PART  of  the  retina.  (KolUker. )  3.50 
diameters. 

1,  pigment-cells  ;  ~,  columnar-cells. 


Fig.  .526.— Fibres  of  the  crystalline 
LENS.     (350  diameters.) 

A,  longitudinal  view  of  the  fibres  of  the  lens  from 
the  ox,  showing  the  serrated  edges.  B,  trans- 
verse section  of  the  fibres  of  the  lens  from  the 
human  eye.  C,  longitudinal  view  of  a  few  of 
the  fibres  from  the  equatorial  region  of  the 
human  lens.  Most  of  the  fibres  in  C  are  seen 
edgewise,  and,  towards  1,  present  the  swell- 
ings and  nuclei  of  the  '  nuclear  zone ' ;  at  2,  the 
flattened  sides  of  two  fibres  are  seen.  A  and 
B  from  KoUiker  ;  C  from  Henle.) 


THE   LENS. 


465 


The  pigmentar}^  layer  is  thickened  over  the  fovea,  and  there  is  also 
a  thickening  in  the  choroid  coat  here,  due  to  a  large  accumulation  of 
capillary  vessels. 

The  pars  ciliaris  retinae,  which  commences  at  the  ora  serrafa,  where 
the  retina  proper  abruptly  ends,  is  composed  of  two  epithelial  layers 
(fig.  524),  and  has  no  nervous  structures.  Of  the  two  layers,  the 
external  is  a  thick  stratum  of  pigmented  epithelium  formed  of  rounded 
cells  and  continuous  with  the  pigmentary  layer  of  the  retina  on  the 
one  hand,  and  with  the  uvea  of  the  iris  on  the  other  ;  the  inner  is  a 
layer  of  columnar  cells,  each  containing  an  oval  nucleus.  They 
probably  represent  the  Mtillerian  fibres  of  the  retina. 


Fig.  527. — Cells  of  vitreous.     (Schwalbe.) 
a,  (!,  without  vacuoles  ;  h,  c,  e,  jt,  g,  with  vacuoles. 

The  retina  contains  but  few  blood-vessels.  The  central  artery  enters 
and  the  vein  leaves  it  in  the  middle  of  the  optic  nerve.  The  larger 
vessels  ramify  in  the  nerve-fibre  layer,  and  there  are  capillary  net- 
works in  this  layer  and  in  the  inner  nuclear  layer.  There  are  peri- 
vascular (lymph)  spaces  around  the  veins  and  capillaries.  The  sensory 
epithelium  receives  no  blood-vessels,  but  is  nourished  from  the  vessels 
of  the  choroid. 

The  lens. — The  lens  is  a  laminated  fibrous  body  inclosed  by  a  trans- 
parent elastic  capsule  to  which,  around  the  circumference,  the  fibres  of 
the  suspensory  ligament  are  attached  (fig.  508).  Immediately  within  the 
capsule,  in  front  and  at  the  sides,  there  is  a  layer  of  cubical  epithelium 
termed  the  epithelium  of  the  capsule,  but  at  the  margin  of  the  lens 
the  cells  become  longer  and  pass  by  a  gradual  transition  into  the 
lens-fibres  (fig.  525).  The  fibres  which  compose  the  lens  are  long  and 
riband-shaped,  with  finely  serrated  edges  (fig.  526,  A) ;  in  transverse 
section  they  appear  prismatic  (B).     Many  of  the  superficial  fibres  are 

2g 


466  THE   ESSENTIALS   OF   HISTOLOGY, 

nucleated  (c),  the  lens-fibres  having  originally  been  developed  by  the 
elongation  of  epithelium-cells. 

The  vitreous  humour. — This  is  composed  of  soft  gelatinous  tissue, 
apparently  structureless  when  examined  in  the  fresh  condition,  but 
containing  fibres  and  a  few  scattered  cells,  the  processes  of  which  are 
often  long  and  varicose,  and  the  cell-bodies  distended  by  large  vacuoles 
(fig.  527).  The  hyaloid  memhrane,  which  invests  the  vitreous  humour, 
is  homogeneous  and  structureless  except  in  the  region  of  the  ciliary 
processes,  where  it  is  fibrous  in  structure,  forming  the  zonule  of  Zinn 
and  spreading  out  into  the  suspensory  ligament  of  the  lens  (fig.  508). 
This  part  of  the  hyaloid  membrane  is  connected  with  a  circular 
fibrous  portion  of  the  vitreous  humour  which  serves  to  give  addi- 
tional firmness  to  the  attachment  of  the  fibres  of  the  suspensory 
ligament  of  the  lens  (Anderson  Stuart). 


OLFACTORY   MEMBRANE.  467 


LESSON   XLIX. 

STRUCTURE  OF   THE  OLFACTORY  MUCOUS  MEMBRANE 
AND   OF  THE  EXTERNAL   AND   MIDDLE  EAR. 

1.  Vertical  sections  of  the  nasal  mucous  membrane.  The  sections  may 
be  carried  either  across  the  upper  turbinate  bone,  after  decalcification  or 
across  the  upper  part  of  the  nasal  septum.  Make  a  sketch  under  the  low 
power.  Notice  the  difference  in  the  character  of  the  epithelium  in  the 
olfactory  and  respiratory  parts  of  the  membrane. 

2.  Teased  preparation  of  the  epithelium  of  the  olfactory  mucous  membrane. 
A  piece  of  the  membrane  is  placed  quite  fresh  in  osmic  acid  (1  per  cent.)  for 
a  few  hours,  and  is  then  macerated  for  two  days  or  more  in  water.  The 
epithelium  is  broken  up  in  dilute  glycerine  ;  the  cells  easily  separate  from 
one  another  on  tapping  the  cover-glass.  Notice  the  two  kinds  of  cells. 
Sketch  some  of  the  cells  under  a  high  power.^ 

3.  Sections  of  the  external  ear  (these  have  been  already  studied  for  the 
cartilage,  Lesson  XII.). 

4.  Sections  across  the  cartilaginous  part  of  the  Eustachian  tube.  Sketch 
under  the  low  power. 

5.  Preparation  of  the  membrana  tympani.  A  piece  of  the  membrane, 
stained  with  magenta  and  gentian  violet  (see  Lesson  IX.,  ^  2),  is  mounted 
flat  in  xylol  balsam  or  dammar. 

Determine  the  composition  of  the  membrane — i.e.  the  several  layers  com- 
posing it — by  focussing  carefully  with  the  high  power. 


THE   OLFACTORY    MUCOUS    MEMBRANE. 

The  olfactory  region  of  the  nasal  fossae  includes  the  upper  and 
middle  turbinate  processes  and  the  upper  third  of  the  septum.  It 
is  covered  by  a  soft  vascular  mucous  membrane  of  a  yellow  colour 
in  man. 

The  epithelium  of  the  olfactory  mucous  membrane  (figs.  528,  529)  is 
very  thick  and  is  composed  of  long  cells,  set  closely  side  by  side  and 
bounded  superficially  by  a  cuticular  lamina,  through  which  the  free 
ends  of  the  cells  project.  The  cells  are  of  two  kinds:  1.  Long 
narrow  spindle-shaped  or  bipolar  nerve-cells  consisting  of  a  larger  part 
or  body  (h),  containing  the  nucleus,  and  of  two  processes  or  poles,  one 

(c)  straight  and  cylindrical  and  extending  to  the  free  surface,  the  other 

(d)  very  delicate  and  varicose,  looking  not  unlike  a  nerve-fibril  and 

^  The  connection  of  the  olfactory  cells  with  the  olfactory  nerve-fibres  is  displayed 
in  embryos,  the  method  of  Golgi  being  employed. 


468 


THE   ESSENTIALS   OF   HISTOLOGY. 


extending  down  towards  the  corium.  The  position  of  the  nuclear 
enlargement  varies,  and  with  it  the  relative  length  of  the  two  processes. 
The  distal  or  free  process  terminates  in  a  small  clear  projection,  which 
passes  beyond  the  cuticular  membrane ;  in  amphibia,  reptiles,  and 
birds,  and  perhaps  also  in  mammals,  it  bears  fine  stiff  hairlike  fila- 
ments. The  proximal  or  varicose  process  becomes  lost  amongst  the 
plexus  of  olfactory  nerve-fibres  at  the  base  of  the  epithelium ;  it  is 
connected  with  one  of  these  fibres,  and  ultimately  passes  through  the 


Fig.  528. — Cells  and  terminal  nerve-fibres  of  the  olfactort  region. 
(Highly  magnified.) 

1,  from  the  frog ;  .'  and  3,  from  man.  In  1  and  ;.' :  -a,  epithelial  cell,  extending  deeply 
into  a  ramified  process  ;  b,  olfactory  cells ;  c,  their  peripheral  rods ;  e,  the  extremi- 
ties of  these,  seen  in  1  to  be  prolonged  into  fine  hairs  ;  d,  their  central  filaments. 
In  3 : — k,  hairlets ;  c,  free  border  of  cell ;  p,  peripheral  process ;  b,  body  of  cell ; 
}(,  nerve-fibre.     1  and  ;,'  from  M.  Schultze  ;  .>  from  v.  Brunn. 

cribriform  plate  of  the  ethmoid  to  end  in  an  arborisation  within  one  of 
the  olfactory  glomeruli  (see  diagram,  fig.  495,  p.  438).  These  cells 
have  been  termed  the  olfactory  cells.  2.  Long  columnar  epithelium  cells 
{(i),  with  comparatively  broad  cylindrical  nucleated  cell-bodies  placed 
next  to  the  free  surface,  and  long,  forked,  and  branching  tail-like  pro- 
cesses extending  down  to  the  corium.  These  are  regarded  not  as 
sensory  epithelium-cells,  but  merely  as  serving  to  support  the  proper 
olfactory  cells.  They  are  the  columnar  or  sustenfacular  cells.  3.  Taper- 
ing cells  are  present,  at  least  in  some  animals,  in  the  deeper  part  of  the 
epithelium.  They  rest  by  their  bases  upon  the  corium,  and  project 
between  the  other  cells,  which  they  assist  to  support. 


OLFACTORY   MEMBRANE.  469 

The  corium  of  the  olfuctory  mucous  membrane  is  also  very  thick 
(fig.  529).  It  contains  numerous  blood-vessels,  bundles  of  the  olfactory 
nerve-fibres  (whioh  are  non-medullated),  and  a  large  number  of  serous 
glands  known  as  Boiiman's  glands  (h),  which  open  upon  the  surface  by 
ducts  which  i)ass  between  the  epithelium-cells. 


Fig.  529. — Section  of  olfactory  mucous  membrane.    (Cadiat.) 
n,  epithelium  ;  b,  glands  of  Bowman  ;  c,  nerve-bundles. 


THE   EXTERNAL   AND    MIDDLE    EAR. 

The  external  ear  proper  (pinna)  is  composed  of  elastic  fibro-cartilage, 
invested  by  a  thin  closely  adherent  skin.  The  skin  'is  covered  by 
small  hairs,  and  connected  with  these  are  the  usual  sebaceous  follicles. 
In  the  lobule  there  is  a  considerable  amount  of  adipose  tissue ;  and 
voluntary  muscular  fibres  are  in  places  attached  to  the  cartilage  of  the 
pinna,  and  are  seen  in  sections. 

The  external  auditory  meatus  is  a  canal  formed  partly  of  cartilage 
continuous  with  that  of  the  pinna,  partly  of  bone.  It  is  lined  by  a 
prolongation  of  the  skin  and  is  closed  by  the  membrana  tympani, 
over  which  the  skin  is  prolonged  as  a  very  thin  layer.  Near  the 
orifice  the  skin  has  hairs  and  sebaceous  glands,  and  the  meatus  is 
also  provided  throughout  the  cartilaginous  part  with  small  convoluted 
tubular  glands  of  a  brownish-yellow  colour,  which  yield  a  waxy 
secretion  (ceruminous  glands).  They  appear  to  represent  modified 
sweat-glands.     They  are  represented  in  fig.  530. 

The  tympanum  is  lined  by  a  mucous  membrane  which  |is  continuous 
through  the  Eustachian  tube  with  the  mucous  membrane  of  the 
pharynx ;  it  is  also  prolonged  into  the  mastoid  cells.     The  epithelium 


470 


THE   ESSENTIALS   OF  HISTOLOGY. 


is  columnar  and  ciliated  in  some  parts,  but  in  others — e.g.  roof, 
promontory,  ossicles,  and  membrana  tympani — -it  is  a  pavement- 
epithelium. 

The  membrana  tympani  is  a  thin  membrane  formed  of  fibrous 
bundles  which  radiate  from  a  central  depression  (umbo).  Within 
the  radial  fibres  are  a  few  annular   bundles.      Coverincr   the   fibrous 


Hair. 


Sebaceous  glauds. 


Root-sheath  of  1 
follicle.  / 


Root  of  hair,     -'-.y,  <^: 


Fig.  530. — Ceruminous  glaxds  and  hairs  of  the  extekxal  ear.     (Griiber.) 


membrane  externally  is  a  thin  layer  continuous  with  the  skin  of  the 
meatus  ;  covering  it  internally  is  another  thin  layer,  derived  from  the 
mucous  membrane  of  the  tympanic  cavity.  Blood-vessels  and  lym- 
phatics are  distributed  to  the  membrane  chiefly  in  the  cutaneous  and 
mucous  layers. 

The  Eustachian  tube  is  the  canal  leading  from  the  tympanum  to 
the  pharynx.     It  is  formed  of  bone  near  the  tympanum,  but  below, 


THE   EUSTACHIAN   TUBE. 


471 


near  the  pharynx,  it  is  bounded  partly  by  a  bent  piece  of  cartilage 
(tig.  531,  1,  2),  partly  by  fibrous  tissue.     The' latter  contains  numerous 


Fig.  531.— Section   across   the   caktilaginous   part   of   the   eustachian 
TUBE.     (Riidinger.) 

1,  2,  bent  cartilaginous  plate  ;  3,  muse,  dilatator  tubse ;  to  the  left  of  i,  part  of  the 
attachnient  of  the  levator  palati  muscle ;  5,  tissue  uniting  the  tube  to  the  base  of  the 
skull ;  e  and  7,  mucous  glands ;  S,  10,  fat ;  9  to  11,  lumen  of  the  tube  ;  12,  connective 
tissue  on  the  lateral  aspect  of  ttie  tube. 


mucous  glands  (6,  7),  which  open  into  the  tube,  and  on  the  outer  side 
a  band  of  muscular  tissue  (3)  which  joins  the  tensor  palati.  The 
epithelium  is  ciliated. 


472  THE   ESSENTIALS   OF   HISTOLOGY. 


LESSOX   L. 

THE  IXTERXAL    EAR. 

1.  SECTION'S  across   one  of  the  membranous  semicii-cular   canals   of   a   fish 
(skate). 

2.  Longitudinal  sections  through  the  ampulla  of  a  semicircular  canal 
(skate). 

1  and  2  may  be  hardened  in  chromic  and  osmic  acid  (see  below  under  .5) 
and  embedded  in  celloidin. 

The  semicircular  canals  and  their  ampulke  may  also  be  seen  cut  across  in 
sections  of  the  petrosal  of  the  guinea-pig  or  other  mammal. 

3.  Golgi  preparations  of  the  macula  of  the  utricle  from  the  skate. 

4.  Teased  preparations  of  the  auditory  epithelium  of  an  ampulla  or  of  the 
macula  of  the  utricle,  from  the  skate. 

5.  Vertical  sections  through  the  middle  of  the  cochlea  of  a  mammal 
(guinea-pig). 

The  cochlea  is  put  quite  fresh  into  0"2  per  cent,  chromic  acid  containing 
one-fifth  its  volume  of  1  per  cent,  osmic  acid,  or  into  Flemming's  solution, 
or  10  per  cent,  formol.  The  decalcification  can  be  effected  by  the  use  of  the 
phloroglucin-nitric  acid  fluid,  or  by  sulphurous  acid.^  When  decalcified,  the 
preparation  is  well  washed,  and  then  transferred  to  alcohols  of  gradually 
increasing  strength. 

In  preparing  sections  of  the  above  three  preparations  it  is  advisable,  in 
order  that  the  epithelium  should  be  kept  in  position,  to  embed  in  celloidin. 
If  the  paraflin  method  of  embedding  be  used,  the  sections  are  fixed  to  the 
slide  by  an  adhesive  process.  The  organ  should  preferably  be  stained  in 
bulk. 

6.  Teased  preparations  of  the  epithelium  of  the  organ  of  Corti  from  the 
guinea-pig. 

Both  4  and  6  are  made  from  osmic  preparations. 

Make  sketches  from  all  these  preparations  under  the  high  power.^ 


The  labyrinth,  which  is  the  essential  part  of  the  auditory  organ, 
consists  of  a  complex  membranous  tube  lined  by  epithelium  and  filled 
with  endolymph,  contained  within  a  bony  tube — the  osseous  labyrinth 
— of  corresponding  complexity  of  shape  (figs.  532,  533).  The  mem- 
branous labyrinth  does  not  wholly  fill  the  bony  cavity ;  the  rest  of  the 
space  is  occupied  by  perilymph.  The  membranous  labyrinth  (fig.  532) 
is  composed  of  the  utricle  (u),  and  the  three  semicircular  canals  (each 

^  See  Appendi.v. 

-For  details  of  the  methods  of  obtaining  the  various  parts  of  the  labyrinth  for 
microscopical  examination,  the  student  is  referred  to  the  author's  Course  of 
Practical  Histology. 


THK    LABYRINTH. 


47* 


with  an  enlargement  or  ampulla  which  opens  into  it),  the  saccule  (s),  and 
the  canal  of  the  cochlea  {ex.). 

The  branches  of  the  auditory  nerve  pass  to  certain  parts  only  of  the 
membranous  labyrinth,  viz.  the  maculae  of  the  utricle  and  saccule,  the 
cristjie  of  the  ampulla^  and  along  the  whole  length  of  the  canal  of 
the  cochlea  (the  shaded  parts  in  fig.  532). 

At  these  places  the  lining  epithelium  is  specially  modified  to  form  a 
sensory  or  nerve-epithelium  ;  elsewhere  it  is  a  simple  pavement- 
epithelium. 

The  membranous  semicircular  canals  and  the  utricle  and  saccule 
are  composed  of  fibrous  tissue,  which  is  adherent  along  one  side  to  the 


Fig.  .^32.— Pl.\n  of  the  bight  mem- 
branous    LABYRINTH     VIEWED     FROM 

THE  MESIAL  ASPECT.       y- 

v.,  utricle,  with  it.s  macula  and  s.s.c,  p.s.c, 
and  e.s.c,  the  three  semicircular  canals 
with  their  ampulla!;  s,  saccule;  aq.v., 
aquseductus  vestibuli ;  s.e.,  saccus  endo- 
lymphaticus;  c.r.,  canalis  reuniens ;  c.c, 
canal  of  the  cochlea. 


Fig.  .533.  —View  of  the  interior  of- 
the  left  osseous  labyrinth. 

The  bony  wall  of  the  labyrinth  is  removed 
superiorly  and  externally.  1,  fovea  hemi- 
elliptica  ;  -2,  fovea  hemisphasrica  ;  8,  com- 
mon opening  of  the  superior  and  posterior 
semicircular  canals ;  4,  opening  of  thfr 
aqueduct  of  the  vestibule  ;  5,  the  superior, 
0,  the  posterior,  and,  7,  the  external  semi- 
circular canals  ;  S,  spiral  tube  of  the  coch- 
lea ;  9,  scala  tympani ;  10,  scala  vestibuli. 


endosteum  of  the  bony  canal ;  from  the  opposite  side  bands  of  fibrous 
tissue  pass  across  the  perilymph  (fig.  534).  Within  the  fibrous  mem- 
brane is  a  thick  clear  tunica  propria,  which,  in  the  semicircular  canals, 
may  form  papilliform  elevations  in  the  interior  of  the  tube  (fig.  535). 

The  places  of  entrance  of  the  nerve-fibres  are  marked  in  each 
ampulla  by  a  transverse,  inwardly  projecting  ridge  (crista),  in  the 
saccule  and  utricle  by  a  thickening  of  the  tunica  propria  (macula). 
The  epithelium  at  these  places  is  formed  of  columnar  cells  (fig.  536), 
which  are  surmounted  by  long,  stiff,  tapering  hairs  {auditm-y  hairs, 
fig.  536,  li).  Around  these  hair-cells  the  axis-cylinders  of  the  nerve- 
fibres  ramify  (fig.  538) ;  they  are  therefore — like  the  gustatory  cells  of 
the  taste-buds — sensory  epithelium  cells.     Between  them  are  a  number 


474 


TEE    ESSENTIALS   OF   HISTOLOGY 


of  thin  and  somewhat  rigid  nucleated  cells  {fibre-cells  of  Retzius),  which 
rest  upon  the  basement-membrane,  and  are  connected  at  their  free 
extremity  with  a  cuticular  membrane,  through  which  the  auditory 
hairs  project. 

The  auditory  hairs  do  not  jut  freely  into  the  endolymph,  but  into  a 
soft  mucus-like  substance,  of  a  dome-like  form  in  the  ampulhie  {cupula 


cL. 


end 


Fig.  534.— Section  of  .v  semicircular  canal,  new-born  child.     (Sobotta.) 

X  55. 

c.t.,  connective  tissue  strands,  between  membranous  canal  and  endosteum  of  bony  canal ; 
III,  membranous  canal ;  ?<,  wall  of  bony  canal ;  c,  remains  of  fiKtal  cartilage  ;  end, 
endosteum  ;  r,  blood-vessels. 


terminals,  fig.  536),  and  which  in  the  saccule  and  utricle  has  a  mass  of 
calcareous  particles  {otoliths)  embedded  in  it. 

The  cochlea  consists  of  a  bony  tube  coiled  spirally  around  an  axis 


THE  COCHLEA. 


475 


Fig.  535. — Sectiox  of  membranous  semicircular  canal.     (Riidinger.) 
(More  magnified.) 
1,  outer  fibrous  layer ;   2,  tunica  propria ;   3,  6,  papilliforin  projections  with  epithelial 
covering ;  5,  fixed  side  of  the  canal,  with  very  thin  tunica  propria  without  papilla? ; 
7,  fibrous  bands  passing  to  periosteum. 


Fig.  536. — Longitudinal  section   of    an    ampulla   through    the  crista 

ACU.STICA  (diagrammatic). 
urap.,  cavity  of  the  ampulla;  sec,  semicircular  canal  opening  out  of  it;  c,  connective 
tissue  attached  to  the  wall  of  the  membranous  ampulla  and  traversing  the  perilymph ; 
e,  f ,  flattened  epithelium  of  ampulla ;  7i,  auditory  hairs  projecting  from  the  columnar 
cells  of  the  auditory  epithelium  into  the  cupula,  cap.Urm  ;  i-,  blood-vessels  ;  n,  nerve- 
fibres  entering  the  base  of  the  crista  and  passing  into  the  columnar  cells. 


476 


THE   ESSENTIALS   OF   HISTOLOGY. 


which  is  known  as  the  columella  (fig.  539,  540).  The  tube  is  divided 
longitudinally  by  a  partition  which  is  formed  partly  by  a  projecting 
lamina  of  bone   {spiral  lamina),    partly  by  a    flat  membrane  {basilar 


ep 


m^^^:^ 


Fig.  537. — Section  of  macula  acustica,  cat.     (Sobotta.)     x  120. 
ep,  epithelium  ;  n,  n,  fibres  of  vestibular  nerve. 


Fig.  538. — Neeve  terminations  in  macula,     golgi  method. 
(Barker,  from  Lenhossek. ) 

membrane),  into  two  parts  or  scalce ;  the  upper  (supposing  the  cochlea 
resting  base  downwards)  being  termed  the  scala  'vestibuli,  the  lower  scala 
tympani ;  the  latter  is  closed  near  its  larger  end  by  the  membrane  of 
the  fenestra  rotunda.  The  scalte  are  lined  by  endosteum,  and  are 
filled  with  perilymph,  continuous  with  that  of  the  rest  of  the  osseous 


THK   (X)CllLEA. 


477 


labyrinth  at  the  commencement  of  the  scala  vestibuli  ;  they  communi- 
•cate  at  the  apex  by  an  opening,  the  helicotrema. 

The  scala  vestibuli  does  not  occupy  the  whole  of  that  part  of  the 
bony  tube  of  the  cochlea  which  is  above  the  partition.     Its  outer  and 


str.v. 


w  a 

Fig.  539. — Section  through  the  cochlea  of  the  cat.     (Sobotta.)     x  25. 

dc,  duct  of  cochlea ;  scv,  scala  vestibuli ;  set,  scala  tympani  ;  w,  bony  wall  of  cochlea ;  C, 
organ  of  Corti  on  membrana  basilaris  ;  mR,  membrane  of  Reissner ;  n,  nerve  fibres  of 
cochlear  nerve  ;  gsp,  ganglion  spirale  ;  str.v.,  stria  vascularis. 


lower  third  is  cut  off  by  a  delicate  connective-tissue  membrane 
{membrane  of  Reissner,  fig.  541,  E),  which  springs  from  near  the  end 
of  the  spiral  lamina,  and  passes  upwards  and  outwards  to  the  outer 
wall,  thus  separating  a  canal  (d.c.)  triangular  in  section,  which  is 
lined  by  epithelium,  and  represents  the  membranous  labyrinth  of  the 
cochlea  {dud  or  canal  of  the  cochlea). 


478 


THE   ESSENTIALS   OF   HISTOLOGY. 


canal  of        scata     membrane  of 
the  cochlea     vestibuli     Reisstier 


gan- 
glion 


gan-      membrane  of 
glion  Reissner 


membrana 
iectoria 


Fig.  540. 


scala        basilar 
tympan  i    membrane 

-Vertical  section  through  the  middle  of  the  human  cochlea. 
(Diagrammatic.) 


Fig.  541. — Vertical  section  of  the  first  turn  op  the  human  cochlea. 

(G.  Retzius.) 

s.v,  scala  vestibuli ;  s.  t,  soala  tympani ;  d.c,  canal  or  duct  of  the  cochlea ;  sp.l,  spiral  lamina ; 

n,  nerve-fibres  ;   <..<!p,  spiral  ligament ;  .s-«)-.r,  stria  vascularis ;   s.s^j,  spiral  sulcus  ;  iJ, 

section  of  Reissner's  membrane  ;  I,  limbus  laminae  spiralis  ;  m.t,  membrana  tectoria; 

tC,  tunnel  of  Corti ;  b.m,  basilar  membrane  ;  li.i,  h.e,  internal  and  external  hair-cells. 


THE   COCHLEA. 


479 


Canal  of  the  cochlea. — The  Hoor  of  the  canal  of  the  cochlea  is  formed 
( I )  of  the  extremity  of  the  spiral  lamina,  which  is  thickened  above  by 
a  peculiar  kind  of  connective  tissue,  forming  an  overhanging  projection 
known  as  the  limlms  (fig.  541,  ^) ;  and  (2)  of  the  basilar  membrane  {h.m.), 
which  stretches  across  from  the  end  of  the  bony  lamina  to  the  outer 
wall,  and  is  attached  to  this  by  a  projection  of  reticular  connective 
tissue  termed  the  spiral  ligament  (l.sp). 


Fig.  542. — A  pair  of  rods  of  corti,  from  thk  habhit'.s  cochlea,  in  side 
VIEW.     (Highly  magnified.) 

6,  b,  basilar  membrane;  i.r.,  inner  rod  ;  e.r.,  outer  rod.     The  nucleated  protoplasmic 
masses  at  the  feet  are  also  .shown. 


Outer  hair-cells. 


Inner    Blood-      Basilar         Outer        ' — r — ' 
rod.      vessel,     membrane.        rod.       Cells  of 
Deiters. 

Fig.  .543. — Section  through  the  organ  of  corti  of  the  human  cochlea. 
(G.  Retzius.)     (Highly  magnified.) 


The  basilar  membrane  is  composed  of  stiff  straight  fibres,  which  extend 
from  within  out,  and  are  embedded  in  a  homogeneous  substance.  The 
membrane  is  covered  below  by  a  layer  of  connective  tissue  continuous 
with  the  endosteum  of  the  scala  tympani ;  above,  the  modified  epi- 
thelium which  forms  the  oi-gan  of  Corti  rests  upon  it.  It  becomes 
gradually  broader  in  the  upper  turns  of  the  cochlea  (rather  more  than 
twice  as  broad  in  the  uppermost  as  in  the  lowermost  turn),  and  its 
constituent  fibres  become  therefore  gradually  longer. 


480 


THE    ESSENTIALS   OF   HISTOLOGY. 


The  organ  of  Corti  consists  of  the  following  structures  : 
1.  The  roiU  of  Corti,  two  series  (inner  and  outer)  of  stiff,  striated 
structures,  of  a  peculiar  shape,  the  inner  somewhat  like  a  human  ulna, 
the  outer  like  a  swan's  head  and  neck  (fig.  542).  They  rest  by  one 
extremity  (the  foot)  on  the  basilar  membrane  a  short  distance  apart, 
and  are  inclined  towards  one  another,  their  larger  ends  (heads)  being 
jointed  together ;  the  series  of  rods  thus  enclose  a  sort  of  tunnel,  the 
floor  of  which  is  formed  by  a  part  of  the  basilar  membrane  (fig.  544). 
Close  to  their  feet  may  usually  be  seen  the  remains  of  the  cells  from 
which  they   have  been   formed.     The  inner  rods   are   narrower   and 


Fig.  544.— Semi-diagrammatic  view  of  part  of  the  basilar  membrane 
and  tunnel  of  corti  of  the  babbit,  from  above  and  the  side. 
(Much  magnified. ) 

I,  lirabus  ;  Cr.,  extremity  or  crest  of  limbus  with  tooth-like  projections  ;  b,  basilar  mem- 
brane ;  sp.l.,  spiral  lamina  with,  p,  perforations  for  transmission  of  nerve-fibres; 
i.r.,  fifteen  of  the  inner  rods  of  Corti;  h.i.,  their  flattened  heads  seen  from  above; 
e.r.,  nine  outer  rods  of  Corti;  h.e.,  their  heads,  with  the  phalangeal  processes  extend- 
ing outward  from  them  and  forming,  with  the  two  rows  of  phalanges,  the  lamina 
reticularis,  I.r. 


rather  more  numerous  than  the  outer.  The  head  of  each  outer  rod 
has  a  process  which  extends  outwards  and  is  known  as  the  phalangeal 
process.     This  forms  part  of — 

2.  A  reticular  lamina  (fig.  544,  I.r.),  which  is  a  cuticular  structure 
extending  like  a  wire-net  over  the  outer  epithelium-cells  of  the  organ 
of  Corti,  and  is  composed  of  two  or  three  series  of  stiff"  fiddle-shaped 
rings  {phalanges)  cemented  together  in  such  a  manner  as  to  leave 
square  or  oblong  apertures  through  which  the  hair-cells  (see  below) 
project. 

3.  The  outer  hair-cells  placed  external  to  the  rods  of  Corti.  These 
are  epithelium-cells  of  columnar  shape,  arranged  in  three  or  four  series 


THE   COCHLEA. 


481 


ffig.  543).  The  tree  extremity  of  the  cell  is  surmounted  by  a  bundle 
of  short  (ludifwi/  hairs,  and  projects  through  one  of  the  apertures  in 
the  reticular  lamina  ;  the  Hxed  extremity  is  prolonged  into  a  stiff 
cuticular  process,  which  is  attached  to  the  basilar  membrane.  Between 
them  are  other  supporting  cells  which  are  tapered  in  the  same  manner, 
but  rest  by  their  larger  end  upon  the  basilar  membrane,  and  are 
prolonged  above  into  a  cuticular  process  which  is  attached  to  the 
reticular  lamina  (cells  of  Deitcrs,  figs.  543,  545). 

4.  The  inner  hair-celU  (fig.  543),  placed  internal  to  the  rods  of  Corti. 
They  form  a  single  series  of  columnar  cells  surmounted  by  auditory 
hairs,  lying  in  close  apposition  to  the  inner  rods. 


Fig.  545. 

Fig.  545. — Four  cells  of  peiters  from  the  rabbit.     (After  G.  Retzius. ) 
(Highly  magnified.) 

The  varicose  lines  are  nerve-fibrils.     The  phalangeal  processes  are  attached  above 
to  a  portion  of  the  lamina  reticularis. 

Fig.  546.— General  view  of  the  mode  of  distribution  of  the  cochlear 

NERVE,    ALL   THE   OTHER   PARTS    HAVING   BEEN    REMOVED.       (Aruold. ) 


The  remaining  epithelium-cells  have  no  important  characteristics. 
They  are  long  and  columnar  next  to  the  outer  hair-cells,  but  soon 
diminish  in  size,  becoming  cubical,  and  in  this  form  they  are  con- 
tinued over  the  outer  wall  of  the  cochlear  canal.  Here  thev  cover 
a  very  vascular  membrane  {stria  vasndaris,  fig.  541,  str.r.),  which  is 
frequently  pigmented ;  its  capillary  blood-vessels  penetrate  between 
the  epithelium-cells.  Internal  to  the  inner  hair-cells  the  epithelium 
also  soon  becomes  cubical ;  it  is  prolonged  in  this  form  over  the  limbus 
of  the  spiral   lamina.     The   epithelium  of  Reissner's  membrane  is  of 

the  pavement  variety. 

2h 


482 


THE   ESSENTIALS   OF   HISTOLOGY. 


The  memhrana  tedoria  (figs.  541,  543)  is  a  soft,  fibrillated  structure, 
which  is  attached  along  the  upper  surface  of  the  limbus,  and  lies 
like  a  pad  over  the  organ  of  Corti.  It  thins  out  towards  the  distal 
margin,  here  becoming  somewhat  reticular,  and,  according  to  Retzius, 


Fig.  .547. — Ending  of  some  of  the  fibres  of  the  cochlear  nerve  amongst 

THE   H.\IR-CELLS,       (G.  EetziuS. ) 

This  preparation   i.s  made  by  Golgi's  method,  and  is  viewed  from  above,     p,  a  cell 
belonging  to  the  spiral  ganglion. 


it  is  attached  to  the  lamina  reticularis.  In  sections  it  usually  appears 
raised  a  short  distance  above  the  auditory  hairs,  but  it  is  probable 
that  it  always  rests  upon  them  during  life. 

The  fibres  of  the  cochlear  branch  of  the  auditory  nerve  enter  the 
base  of  the  columella,  and  run  in  canals  through  its  substance  (figs. 
539,  5  40),  being  gradually  deflected  outwards  as  they  pass  upwards 
into  the  spiral  lamina,  at  the  base  of  which  they  swell  out  into  a 
ganglionic  cord  {spiral  ganglion).  The  fibres  take  origin  from  the  cells 
of  this  ganglion. 


THE   COCHLEA.  483 

After  traversing  the  spiral  lamina  they  emerge  in  bundles,  and 
the  fibres  then,  having  lost  their  medullary  sheath,  pass  into  the 
epithelium  of  the  inner  hair-cell  region.  Here  some  of  them  course  at 
right  angles  and  are  directly  applied  to  the  irmer  hair-cells,  whilst 
others  cross  the  tunnel  of  Corti,  to  become  applied  in  like  manner 
to  the  outer  hair-cells  and  the  cells  of  Deiters  (figs.  543,  545).  They 
apparently  lie  between  and  in  close  contact  with  those  cells,  but  there 
does  not  appear  to  be  any  direct  continuity  between  the  nerve-fibrils 
and  the  cell-substance. 


484  THE   ESSENTIALS  OF   HISTOLOGY. 


APPENDIX. 


Mounting  solutions  ;—  1.  Normal  saline  solution.—  A  0'6  to  0"9  per  cent, 
solution  of  common  salt  is  used  in  place  of  serum  for  mounting  fresh 
tissues  for  immediate  examination.  The'  lower  percentage  is  used  for 
frog's  tissues,  the  higher  for  mammals'.  Preparations  mounted  in  salt 
solution  cannot  be  preserved  permanently. 

2.  Glycerine,  diluted  with  an  equal  quantity  of  water.  The  cover-glass 
may  be  fixed  by  gold  size. 

3.  Canada  balsam,  from  which  the  volatile  oils  have  been  driven  oflf  by 
heat,  dissolved  in  xylol. 

4.  Dammar  varnish,  made  by  dissolving  dammar  resin  in  xylol.  The 
solution  is  filtered  through  paper  wetted  with  chloroform.  This  is  used  for 
the  same  purposes  as  xylol  balsam  and  has  the  advantage  of  remaining 
colourless,  whereas  Canada  balsam  becomes  yellow  after  long  keeping. 

5.  Acetate  of  potassium,  a  nearly  saturated  solution.  This  is  the  best 
medium  for  osmic  preparations  and  for  iodine-stained  liver,  to  show 
glycogen  within  the  cells.  The  cover-glass  may  be  fixed  by  soluble  glass 
or  by  gold  size. 

General  methods  of  preserving  and  hardening  tissues  and  organs.^— 
The  following  fluids  may  be  used  : — Alcohol  (75  per  cent,  to  absolute)  ; 
acetone  ;  Carnoy's  fluid  (absolute  alcohol  60  c.c,  chloroform  30  c.c,  glacial 
acetic  acid  10  c.c.) ;  formol  (diluted  with  from  9  to  99  parts  of  water)  ; 
corrosive  sublimate  (saturated  solution  in  water  or  spirit)  ;  chromic  acid 
solution  (1  in  200  to  1  in  500,  to  which  glacial  acetic  acid  may  advantageously 
be  added  in  the  proportion  of  2  parts  acetic  acid  to  1000  chromic  solution) ; 
picric  acid  solution  (saturated,  either  alone  or  containing  2  parts  of  nitric  or 
sulphuric  acid  to  1000) ;  Mann's  fluid  (a  mixture  of  equal  parts  of  saturated 
aqueous  solutions  of  mercuric  chloiide  and  picric  acid)  ;  osmic  acid  solution 
(1  per  cent.)  ;  bichromate  of  potassium  solution  (3  per  cent.),  to  which  for 
more  rapid  hardening  glacial  acetic  acid  may  be  added  to  the  extent  of  5  per 
cent,  or  less  ;  Muller's  fluid  (bichromate  of  potash  2|  parts,  sulphate  of  soda 
1  part,  water  100  parts)  ;  Zenker's  fluid  (which  is  Miiller's  fluid  containing 
5  parts  per  cent,  of  mercuric  chloride,  to  which  5  c.c.  of  acetic  acid  is  added 
at  the  time  of  using);  and  mixtures  of  Muller's  fluid  and  osmic  acid  1  per 
cent,  in  varying  proportions. 

1  Details  of  the  methods  of  preparing  fixing  and  staining  solutions  as  well  as  a 
discussion  of  the  theory  of  their  action  will  be  found  in  Mann's  Physiological  Histology, 
Oxford,  1902. 


APPENDIX.  485 

It  is  best,  if  possible,  to  inject  the  fluid  used  for  hanleninc,'  into  the  blood- 
vessels after  washing  them  out  with  warm  normal  saline ;  if  this  is  not 
passible,  very  small  pieces  of  tissue  should  be  taken,  and  always  a  consider- 
able amount  of  tlie  hardening  fluid. 

The  fluid  of  most  univ^ei'sal  application  is  formol.  This  is  a  40  per  cent. 
solution  of  formaldehyde.  Mi.xed  in  the  proportion  of  10  parts  formol  to 
90  water,  it  penetrates  readily  and  hardens  quickly.  The  tissue  may  remain 
in  formol  a  few  days  and  should  then  be  transferreil  to  alcohol.  For  rapi<l 
rt\ation  a  very  small  piece  of  the  tissue  is  placed  in  10  per  cent,  formol 
and  warmed  to  a  temperature  of  about  40'  or  .50"  ;  it  will  be  sufficiently 
liardened  in  half  an  Iiour,  and  may  then  be  transferred  first  to  weak  and 
then  gradually  to  absolute  alcohol,  so  that  it  is  ready  for  the  preparation  of 
sections  in  about  an  hour. 

Pure  acetone  is  also  of  utility  for  rapid  fi.xatiou  and  hardening.  Small 
pieces  of  the  tissue  are  dropped  into  a  large  amount  of  acetone,  which  not 
only  fixes  and  hardens  but  also  dehydrates,  so  that  the  tissue  can  be  trans- 
ferred in  an  hour  or  so  direct  to  molten  paraffin  for  embedding.  But  much 
better  results  are  got  by  placing  in  10  per  cent,  formol  for  thirty  minutes 
before  transferring  to  acetone. 

For  preserving  the  structure  of  cells  and  nuclei,  one  of  the  best  fixing 
fluids  is  that  recommended  by  Flemming.  This  consists  of  15  vols,  of  1  per 
cent,  chromic  acid,  4  vols,  of  2  per  cent,  osmic  acid,  and  1  vol.  glacial  acetic 
acid.  It  must  be  freshly  pi-epared.  It  is  sometimes  diluted  with  from  two 
to  five  times  its  bulk  of  water  before  use.  One  or  two  days  is  sufficient  for 
fixaticm  and  hardening.  The  tissue  should  be  washed  for  several  hours  in 
running  water  after  removal  from  the  mixture,  and  then  placed  in  dilute 
alcohol.  Carnoy's  fluid  is  in  many  cases  excellent  for  cell-structure  and 
mitotic  changes,  and  very  rapid  in  its  action. 

Tissues  to  be  hardened  in  alcohol  are  usually  placed  at  once  in  absolute 
alcohol,  but  for  some  tissues  it  is  best  to  begin  with  50  per  cent,  alcohol, 
and  pass  the  pieces  through  successive  grades  of  75  per  cent.,  95  per  cent., 
into  absolute  alcohol,  leaving  them  a  few  hours  in  each.  They  are  ready  for 
cutting  as  soon  as  they  are  dehydrated,  but  as  a  rule  they  may  be  left 
a  long  time  in  alcohol  without  deterioration.  Organs  which  contain  much 
fllirous  tissue,  such  as  the  skin  and  tendons,  should  not  go  into  stronger 
alcohol  than  about  80  or  90  per  cent.  ;  otherwise  they  become  too  hard 
to  cut.  Alcohol  is  generally  used  after  the  other  fixing  reagents,  partly 
to  complete  the  hardening,  partly  on  account  of  its  dehydrating  property, 
since  previous  to  embedding  in  paraffin  all  trace  of  water  must  be  eliminated 
from  the  tissue.  If  mercuric  chloride  be  used  for  hardening,  tincture  of 
iodine  must  be  added  to  the  alcohols  subseijuently  used  (except  tlie  final 
alcohol),  to  get  rid  of  the  excess  of  sublimate.  Mercuric  chloride  in  alcohol 
(saturated  solution)  is  one  of  the  most  rapid  fixing  and  hardening  reagents, 
and  may  be  used  if  sections  are  desired  within  a  very  short  time.  It  can  also 
be  used  in  place  of  alcohol  and  ether  mixture  for  fixing  blood  films  (Lesson  II. 
>;  5),  in  which  case  it  may  be  saturated  with  eosin,  and  used  for  fixing  and 
staining  at  the  same  time.     An  immersion  of  5  minutes  is  sufficient. 


486  THE   ESSENTIALS   OF   HISTOLOGY. 

Many  tissues  can  be  instantly  hardened  by  being  plunged  for  a  minute 
into  boiling  water  and  then  placed  in  alcohol  :  this  is  not,  however,  a  good 
method  for  glandular  organs. 

For  tissues  that  are  to  be  hardened  in  chromic  acid  an  immersion  of  from 
seven  to  fourteen  days  is  generally  necessary  ;  they  may  then,  after  washing 
for  some  hours  or  days  in  tap-water,  be  placed  in  alcohol  for  preservation 
and  to  complete  the  process  of  hardening.  The  alcohol  should  be  changeil 
once  or  twice. 

Organs  placed  in  bichromate  of  potassium  or  Midler's  fluid  are  ready  for 
section  in  a  fortniglit  or  three  weeks  ;  they  may,  however,  be  left  for  a 
much  longer  time  in  those  fluids  without  deterioration. 

With  picric  acid  the  hardening  process  is  generall}  complete  in  two 
or  three  days ;  the  organs  may  tlien  be  transferred  to  alcohol,  which 
ought  to  be  frequently  changed. 

The  hardening  of  the  brain  and  spinal  cord  in  Mliller's  fluid  takes  fiom 
three  weeks  to  as  many  months.  It  can  be  hastened  by  warmth,  and -by 
the  addition  of  acetic  acid,  or  by  placing  small  pieces  in  Marchi's  solution 
(see  below),  after  they  have  been  a  week  or  ten  days  in  Midler's  fluid. 

Tissues  containing  calcai'eous  matter,  e.g.  bone  and  tooth,  may  be  rapidly 
decalcified  in  a  .solution  made  by  dissolving,  with  the  aid  of  heat,  1  grm. 
phloroglucin  in  10  c.c.  nitric  acid,  and  filling  up  to  100  c.c.  with  water, 
to  which  more  nitric  acid  may  be  added  if  desired.  Another  rapid  decalci- 
fying fluid  is  commercial  sulphurous  acid  solution.  If  it  is  desired  to 
preserve  the  soft  parts  within  the  bone,  it  should  first  be  placed  for  a 
few  hours  in  10  per  cent,  formol.  For  decalcifying  more  slowly  a  1  to 
5  per  cent,  solution  of  nitric  acid  in  water  or  alcohol,  a  saturated  solution 
of  picric  acid  containing  a  superabundance  of  crystals,  or  a  1  per  cent, 
solution  of  chromic  acid  are  employed. 

Embedding  of  hardened  tissues,  and  preparation  of  sections.— 
Sections  are  most  advantageously  made  with  some  form  of  microtome.  It 
is  generally  needful  to  support  the  hardened  tissue  whilst  it  is  being  cut, 
and  with  this  object  it  is  embedded  in  some  substance  which  is  applied 
to  it  in  the  fluid  condition  and  becomes  solid  on  standing.  The  embedding 
substance  can  either  simply  inclose  the  tissue,  or  the  tissue  may  be  soaked 
in  it ;  the  latter  method  is  the  one  commonly  employed. 

The  embedding  substance  chiefly  used  is  paraffin  of  about  50"  C.  melting 
point. 

Embedding  in  paraffin. — Before  being  soaked  in  melted  paraffin,  the 
piece  of  tissue  may  be  stained  in  bulk  ;  it  is  then  dehydrated  b\'  ;i, 
.series  of  alcohols  (50  per  cent.,  75  per  cent.,  95  per  cent.),  finishing  up 
with  absolute  alcohol;  after  which  it  is  soaked  in  cedar-wood  oil,  xylol, 
or  chloroform.  It  is  now  transferred  to  molten  paraffin,  which  should 
not  be  too  hot,  and  is  soaked  in  this  for  one  or  several  hours,  according 
to  thickness.  Very  delicate  objects  are  sometimes  passed  thi^ough  a 
solution  of  paraffin  in  chloroform.  When  thoroughly  impregnated  with 
the  paraffin  the  object  is  placed  in  a  mould  or  glass  which  has  been 
smeared   with   glycerine,   and   is   covered   with    molten   paraffin   which   is 


APPENDIX.  487 

allowed  to  (.ool  quickly.  A  .s(iuare  block  of  the  paiattiu  containing  the 
tissue  is  then  fixed  in  the  desired  position  on  the  microtome,  thin 
sections  are  cut  and  fixed  to  a  slide  (see  below),  the  parafKn  dissolved 
out  by  turpentine  or  xylol,  and  the  sections  mounted  in  Canada  balsam 
or  dammar. 

If  it  be  desired  to  cut  a  ril)and  of  successive  sections,  and  the  paraffin 
used  prove  too  hard  for  them  to  stick  to  one  another  at  the  edges,  a 
})arafiin  of  lower  melting  point  (40°  C.)  is  smeared  over  the  opposite  sides 
of  the  block  ;    the  sections  then  adhere  together  as  they  are  cut. 

Preparatinn  of  frozen  sections. — The  bichromate  solutions  and  formol  are 
the  best  fluids  to  use  for  preserving  tissues  which  are  to  be  frozen  in 
place  of  being  embedded.  The  tissue  requires  to  be  soaked  in  gum-water 
before  being  placed  upon  the  freezing  microtome.  A  thin  syrup  of 
either  gum  arable  or  dextrin  may  be  used. 

Embedding  in  ceUoidin— The  piece  to  be  embedded  is  dehydrated  by 
alcohol,  and  is  then  placed  over  night  in  a  solution  of  celloidin  in  alcohol 
and  ether  similar  to  ordinary  collodion,  and  afterwards  in  collodion  of 
double  strength.  After  twenty-four  hours  more  it  is  removed  from  the 
celloidiu  (collodion)  and  placed  upon  a  wood  or  metal  holder.  When  tlie 
celloidin  is  set  by  evaporation  of  its  ether  the  holder  is  plunged  in 
alcohol  (85  per  cent),  and  after  a  few  hours  sections  may  be  cut  with  a 
knife  wetted  with  spirit  of  the  same  strength.  The  sections  are  placed 
in  95  per  cent,  alcohol ;  then  passed  through  cedar-wood  oil  or  bergamot 
oil  into  xylol  balsam.  They  must  not  go  into  clove-oil,  nor  into  absolute 
alcohol.  The  advantage  of  the  method  is  that  the  celloidin,  which  is 
quite  transparent,  need  not  be  got  rid  of  in  mounting  the  sections,  and 
serves  to  keep  the  parts  of  a  section  together  ;  it  is  thus  very  useful  for 
friable  tissues  or  for  large  sections.  The  tissue  may  either  be  stained  in 
Itulk  liefore  embedding,  or  the  sections  may  be  stained. 

Microtomes. — A  section-cutting  apjsaratus  or  microtome  is  essential  for 
histological  work.  Useful  instruments  for  students  are  the  Cathcart  micro- 
tome for  freezing  and  the  tripod  microtome  for  objects  which  have  been 
embedded  in  paraffin. 

The  tripod  microtome  is  a  simple  and  efficient  little  instrument,  and  has 
the  advantage  of  being  inexjjensive.  It  consists  of  a  metal  frame  (fig.  548) 
in  which  the  razor  is  fixed,  provided  with  a  micrometer  screw  by  which 
the  height  of  the  razor-edge  is  adjusted.  The  paraffin  block  containing  the 
tissue  is  fixed  by  the  aid  of  heat  on  a  fiat  piece  of  glass  over  which  the 
tripod  slides.     The  razor-edge  is  lowered  after  each  successive  section. 

In  the  Cathcart  freezing  microtome  (fig.  549)  the  tissue,  after  being  soaked 
in  gum- water,  is  placed  on  a  metal  ])late  and  frozen  by  playing  an  ether- 
spray  on  the  under  surface  of  the  plate.  The  plate  is  moved  upwards  by  a 
finely-cut  screw,  and  the  knife  or  plane  used  to  cut  the  sections  is  guided 
over  the  plate  by  passing  over  glass  slips.  In  the  Williams  microtome  the 
freezing  agent  is  ice  and  salt  mixture.  In  using  any  freezing  microtome, 
especially  for  the  nervous  system,  it  is  important  not  to  freeze  the  tissue 
too  hard,  or  the  section  will  roll  up. 


488 


THE   ESSENTIALS   OF   HISTOLOGY. 


Somewhat  more  expensive  and  complicated,  but  also  more  efficient,  instru- 
ments are  tlie  rocking  microtome  of  the  Cambridge  Scientific  Instrument 
Company  and  the  microtomes  designed  by  C.  S.  Minot  and  by  Delcpine.    The 


Fig.  .548.— Tripod  microtome.     (Birch's  pattern.) 


Fig.  549. — Cathcart  freezing  microtome. 


APPENDIX. 


489 


actimi  of  all  of  these  is  automat  if.  For  example,  with  the  rocker  microtome 
every  to-and-fro  movement  of  the  handle,  ii,  not  only  cuts  a  section  of  the 
tissue  of  delinito  thickness,  Imt  also  moves  tlie  parallin  block  forwards  in 
readiness  for  the  next  section.      And   by  employing  a  rectangular  block  of 


Fig.  550. — Rocking  microtome. 


Fig.  551.— Minots  automatic  kotary  mickotome. 


490 


THE   ESSENTIALS   OF   HISTOLOGY. 


paraitiii  of  the  proper  consistency,  a  long  series  of  sections  of  the  same 
object,  of  equal  thickness,  can  be  obtained  and  made  to  adhere  together  in 
a  riband  (as  shown  in  fig.  550).     The  sections  can  be  kept  in  series  upon 


Fig.  552.— Minot's  pkecfsion  microtome.    This  is  especiall\-  adapted  for  large  sections. 


Fig.  553.  — Inclined  plane  microtome. 


APPENDIX.  491 

the  slide  bv  the  eniplo>'inent  of  some  adhesive  method  of  mounting  tlie 
riband. 

For  eelloidin-embedded  prepaiations  it  is  necessary  to  cut  the  sections 
with  a  knife  kept  wetted  with  sjnrit.  For  this  purpose  a  sliding  micro- 
tome, in  whicli  tlie  knife  or  razor  is  moved  liorizontally  over  the  tissue, 
with  the  edge  obliquely  inclined  to  the  direction  of  movement,  is  the  most 
useful.  The  best  instrument  for  this  purpose,  especially  for  large  sections 
of  brain,  is  one  in  which  the  celloidin-soaked  object  is  imniersetl  in  spirit 
during  the  actual  process  of  making  the  sections.  It  is  all-important  for 
every  kind  of  microtome  that  the  knife  should  be  in  perfect  order. 

Methods  of  mounting  in  xylol  balsam  or  dammar.— Individual  paraffin- 
cut  sections  or  ribands  of  sections,  such  as  are  cut  with  the  rocking  and 
other  microtomes,  are  fixed  to  a  slide  or  cover-glass — preliminary  to  being 
treated  with  stains  and  other  fluids— in  the  following  way  : — The  slide  (or 
cover-glass),  after  having  been  carefully  cleaned,  is  smeared  very  thinly  with 
fresh  white  of  egg  :  this  can  be  done  with  the  finger  or  with  a  clean  rag, 
and  the  slides  may  be  })ut  aside  to  dry,  protected  from  dust.  It  is  con- 
venient to  prepare  a  large  number  of  slides  at  a  time  in  this  way,  and  to 
keep  them  at  hand  in  a  suitable  receptacle.  When  required  for  use  a  little 
water  is  poured  on  to  the  slide  and  the  riband  of  sections  is  placed  on  the 
water,  which  is  then  warmed  on  a  hot  plate  or  over  a  small  flame  until  the 
paraffin  becomes  flattened  out,  without  actually  melting.  The  water  is  then 
di'ained  oft',  the  slide  put  in  a  warm  place  for  the  remainder  of  the  water  to 
evaporate  (this  will  take  from  half  an  hour  to  an  hour  according  to  the 
size  of  the  section  and  the  temperature  at  which  it  is  kept),  and  then  heated 
sufficiently  to  melt  the  paraffin.  It  is  next  immersed  in  xylol  to  remove 
the  paraffin,  aftei'  which  the  sections  may,  if  already  stained,  be  mounted  at 
once  in  xylol  balsam  or  dammar  ;  if  not  stained,  treat,  after  xylol,  first  with 
absolute  and  then  witli  gradually  lower  grades  of  alcohol,  then  water,  and 
then  stain  and  finall}'  pass  through  water,  alcohol  (in  grades),  clove-oil, 
and  xylol,  into  xylol  balsam  or  damniar.  For  many  sections  some  of  the 
grades  of  alcohol  can  be  omitted,  but  it  is  always  best  to  jalace  in  50  per 
cent,  between  water  and  absolute  alcohol. 

A  simpler  method,  but  one  which,  in  most  cases,  answers  tlie  purpose 
peifectly  well,  is  to  place  the  riband  or  the  individual  sections  cut  from 
paraffin  on  the  surface  of  water  in  a  basin,  just  sufficiently  warm  to  flatten 
out  the  paraffin,  but  not  to  melt  it,  then  pass  a  perfectly  clean  slide  under 
the  surface  of  the  water  and  float  the  sections  on  to  it ;  remove,  drain  off 
the  water,  and  put  the  slide  and  sections  aside  for  one  or  more  hours  until 
all  the  water  has  evaporated.  The  sections  ai'e  found  to  have  adhered 
firmly  to  the  slide  (they  may,  if  desired,  be  yet  more  firmly  fixed  by  drawing 
a  brush  moistened  with  solution  of  celloidin  in  oil  of  cloves  over  them). 
The  paraffin  can  now  be  removed  by  washing  the  slide  with  xylol  or 
immersing  it  in  xylol.  If  not  previously  stained  they  can  then  be  passed 
through  alcohols  and  stained  and  mounted  as  just  described.  It  is  con- 
venient to  keep  the  several  solutions  which  are  required  in  cylindrical 
tubes  or  grooved  glass  receptacles  in  a  regular  row  upon  the  working  table, 


492  THE   ESSENTIALS   OF   HISTOLOGY. 

and  transfer  the  slide  from  one  to  the  other  in  succession.  Tluis  such  a 
series  wouhl  be  (1)  xylol  ;  (2)  absolute  alcohol  ;  (3)  75  per  cent,  alcohol  ; 
(4)  50  per  cent,  alcohol  ;  (5)  distilled  water  ;  (6)  staining  solution  ;  (7)  tap 
water  ;  (8)  distilled  water  ;  (9)  50  per  cent,  alcohol  ;  (10)  75  per  cent, 
alcohol  ;  (11)  absolute  alcohol  ;  (12)  clove  oil  or  xylol.  The  changes  can 
also  be  effected  by  pouring  the  solutions  over  the  sections  and  draining  off, 
but  this  is  less  satisfactory. 

The  following  table  shows  the  methods  which  may  be  adopted  fcjr   the 
treatment  of  paraftin-cut  sections  or  libands  of  sections : 

1.  Place  on  a  slide  or  cover-glass  in  a  drop  of  tap-water : 

the  glass  may  previously  have  been   smeared  with 
egg-white  :  warm  gently. 

2.  Drain  off  water  and  allow  to  dry  completely. 

i 
.3.    Warm  until  paraffin  is  just  melted. 

I 
4.    Dissolve  paraffin  away  with  xylol. 

If  tissue  is  already  stained  in  bulk.  If  tissue  is  not  already  stained. 

I  ~  i 

Mount  in  xylol  balsam  or  dammar.  5.    Absolute  alcohol. 

6.  Descending  grades  of  alcohol. 

7.  Stain. 
For  sections  out  by  tiie  J'reezi?ig  \ 

or    celloidin    methods,    if    the  8.  Water. 

tissue  has  already  been  stained  | 

in  bulk,  the  sections  need  only  9.    Ascendirg  grades  of  alcohol. 

be  put  through  the  ascending  | 

grades  of  alcohol  and  bergamot  10.   Xylol    or     bergamot    oil    or 

oil,     and     then     mounted     in  creosote  or  clove-oil. 

dammar.      If   the    tissue    has  | 

not  already  been  stained,  begin  Mount    in    xylol    balsam    or 

at  No.  7.  dammar. 

Staining  of  sections. — The  fluids  most  commonly  employed  for  the 
staining  of  sections  are  : — (1)  Solutions  of  ha^matoxylin  and  alum  ;  (2) 
solutions  of  carmine  with  or  without  alum  ;  (3)  certain  aniline  dyes.  The 
time  of  immersion  in  the  staining  fluid  varies  according  to  the  strength 
of  the  fluid  and  the  mode  by  which  the  tissue  has  been  hardened.  The 
necessity  of  staining  sections  may  be  avoided  if  the  tissue  is  stained  in 
bulk  before  embedding.  For  this  purpose  a  piece  of  tissue  is  left  to  stain 
for  twenty-four  hours  or  more  in  a  moderately  diluted  hsematoxylin  solution 
or  in  carmalum  or  borax  carmine,  and  is  then  embedded  and  cut  into  sections 
by  the  paraffin  or  freezing  methods.  If  the  latter  be  employed  the  sections 
are  thoroughly  washed  with  tap-water,  dehydrated  by  alcohol,  and  passed 
through  clove-oil  or  xylol  into  xylol  balsam  or  dammar.  For  some  purposes 
(e.g.  the  study  of  ossifying  cartilage)  an  alcoholic  solution  of  magenta  is 
useful  for  staining  in  bulk  ;  from  this  the  tissue  goes  direct  into  a  small 
quantity  of  oil  of  cloves,  and  after  being  soaked  with  this  it  is  passed  into 
molten  paraffin.  Sections  may  also  be  stained  whilst  still  infiltrated  with 
paraffin  by  floating  them  on  to  the  surface  of  the  staining  solution,  which 


APPENDIX.  493 

limy  be  geiitlv  warmed  (but  not  enough  to  melt  tlie  paraffin).  They 
generally  require  far  longer  exjjosure  to  the  stain.  The  subsequent  treat- 
ment is  quite  sini|)le,  for  they  neeil  only  be  transferred  to  warm  water, 
floated  on  to  a  slide  and  allowed  to  dry.  The  parattin  is  then  melted, 
dissolved  away  with  xylol,  and  the  sections  are  mounted  in  dammar. 

The  following  are  some  of  the  principal  staining  solutions  and  methods  of 
staining  for  special  purposes  : 

1.  Delafield's  hcematoxi/lin. — To  150  ciil)ic  centimetres  of  a  saturated 
solution  of  potash  alum  in  water  add  4  cubic  centimetres  of  a  saturated 
solution  of  hsematoxylin  in  alcohol.  Let  the  mixture  stand  eight  days, 
then  decant,  and  add  25  cubic  centimetres  of  glycerine,  and  25  cubic 
centimetres  of  methylic  alcohol.  The  solution  must  stand  a  few  days 
before  it  is  ready  for  use. 

To  stain  sections  add  a  few  drops  of  this  solution  to  a  watch-glassful 
of  distilled  water.  If  overstained  the  excess  of  colour  can  be  removed  by 
alcohol  containing  1  per  cent,  nitric  or  hydrochloric  acid.  With  long 
keeping  this  solution  becomes  red  instead  of  blue  ;  a  trace  of  ammonia 
will  restore  the  blue  colour. 

2.  ElviiicKs  hoimato.vylin. — Dissolve  2  grammes  luematoxylin  (or,  better, 
hfematein)  in  100  cubic  centimeti'es  alcohol  ;  add  100  cubic  centimetres 
water,  100  cubic  centimetres  glycerine,  and  10  cubic  centimetres  glacial 
acetic  acid :  add  potash  alum  to  saturation.  This  solution  will  keep 
almost  indefinitely  :  it  is  valuable  for  staining  in  bulk,  as  it  tloes  not 
easily  overstain.  For  staining  sections  it  is  best  to  dilute  the  solution 
either  with  distilled  water  or  with  30  per  cent,  alcohol.  After  the  sections 
have  been  stained  they  must  be  thoroughly  washed  with  tap-water.  This 
develops  the  blue  colour  of  the  hjematoxylin. 

3.  Kultschitzky^s  hceinatoxylin. — Dissolve  1  gramme  hfematoxylin  in  a  little 
alcohol,  and  add  to  it  100  cubic  centimetres  of  a  2  jjer  cent,  solution  of  acetic 
acid.  This  solution  is  valuable  foi-  staining  sections  of  the  nervous  system 
(see  Weigert-Pal  process). 

4.  Ucemalum. — Hsematoxylin-alum  solutions  acquire  their  colouring 
properties  only  as  the  hsematoxylin  on  keeping  becomes  converted  into 
hseraatein.  The  latter  substance  may,  therefore,  as  recommended  by  Mayer, 
be  used  advantageously  in  place  of  hpematoxylin  if  the  stain  is  required 
immediately.  The  following  mode  of  preparing  the  solution  may  be 
adopted  : — Dissolve  50  grammes  of  ammonia  alum  in  1  litre  of  water,  and 
1  gramme  of  hsematein  in  100  c.c.  of  rectified  spirit.  Add  the  hsematei'n 
solution  gradually  to  the  alum.  The  mixture  is  ready  for  staining  at  once, 
either  as  it  is  or  diluted  with  distilled  water.  A  small  piece  of  thymol  or  a 
little  carbolic  acid  should  be  added  to  prevent  the  growth  of  moulds. 

5.  R.  Heidenhain's  method. — After  hardening  in  alcohol,  or  in  saturated 
solution  of  picric  acid  and  then  in  alcohol,  place  the  tissue  from  twelve 
to  fourteen  hours  in  a  ^  per  cent,  watery  solution  of  hematoxylin,  and  then 
from  twelve  to  twenty-four  hours  more  in  a  h  per  cent,  solution  of  yellow 
chromate  of  potash,  which  may  be  changed  more  than  once.  Then  wash  in 
water,  place  in  alcohol,  pass  through  xylol,  and  embed  in  paraffin. 


494  THE   ESSENTIALS   OF   HISTOLOGY. 

6.  J/.  HeidenhaMs  method. — Harden  in  sublimate,  followed  by  alcohol  ; 
fix  sections  to  slide  by  water  method  ;  treat  with  iodised  alcohol,  transfer  to 
2"5  per  cent,  iron-alum  (solution  of  sulphate  (or  tartrate)  of  iron  and 
ammonia)  and  leave  a  quarter  of  an  hour  or  longer  ;  rinse  with  distilled 
water;  place  in  1  to  0'5  per  cent,  pure  hoematoxylin  in  water  containing 
10  per  cent,  alcohol  for  a  few  minutes  ;  wash  with  water  ;  differentiate  in 
the  iron  and  ammonia  solution  until  nearly  decolorised  ;  wash  for  fifteen 
minutes  in  tap- water ;  dehydrate  and  mount  in  the  usual  way.  This 
method  is  especially  adapted  for  exhibiting  the  centrosomes  of  cells.  It  is 
also  useful  for  retiform  tissue  and  glands. 

Both  the  process  of  mordanting  with  iron-alum  and  the  subsequent 
staining  with  luematoxylin  may  be  considerably  prolonged  with  advantage 
for  some  tissues. 

7.  Carmalum  (Mayer). — Useful  either  for  sections  or  bulk-staining.  If 
the  sections  are  subsequently  passed  through  alcohol  containing  picric  acid 
in  solution  a  double  stain  is  produced. 

Carminic  acid, 1  gramme. 

Ammonia  alum,    -         -         -         -         -         -         -       10  grammes. 

Distilled  water, 200  c.c. 

Boil  together,  allow  to  cool  and  filter.     Add  thymnl  or  a  little  carljolic  acid 
to  prevent  the  growth  of  moulds. 

8.  Canninate  of  ammonia. — Prepared  by  dissolving  carmine  in  ammonia, 
and  allowing  the  excess  of  ammonia  to  escape  by  slow  evaporation.  The 
salt  should  be  allowed  to  dry  and  be  dissolved  in  water  as  required. 

9.  Picric  acid. — A  saturated  solution  of  picric  acid  in  spirit  may  be  used 
as  a  second  stain  after  htematoxylin  or  carmine.  Any  excess  of  picric  acid 
is  dissolved  o\it  by  rinsing  with  strong  spirit.  This  form  of  double  stain  is 
valuable  for  exhibiting  keratinised  tissues  and  muscle-fibres. 

10.  Picro-carminate  of  ammonia,  a  double  stain.  a.  Ranvier's  picro- 
carmine. — To  a  saturated  solution  of  picric  acid  add  a  strong  solution  of 
carmine  in  ammonia,  until  a  precipitate  begins  to  form.  Evaporate  on 
the  water  bath  (or,  better,  allow  it  to  evaporate  spontaneously)  to  one  half 
its  bulk  ;  add  a  little  carbolic  acid  to  pievent  the  growth  of  moulds  ; 
filter  from  the  sediment. 

/3.  Bourne's  picro-carmine. — "  Add  5  c.c.  of  ammonia  to  2  grammes  carmine 
in  a  bottle  capable  of  containing  about  250  c.c.  Stopper,  shake,  and  put 
aside  till  next  day.  Add  slowly,  shaking  the  while,  200  c.c.  of  a  saturated 
solution  of  picric  acid  in  distilled  water.  Put  aside  till  next  day.  Add 
slowly,  constantly  stirring,  1 1  c.c.  of  5  per  cent,  acetic  acid.  Put  aside  till 
next  day.  Filter  ;  to  the  filtrate  add  four  drops  of  ammonia,  put  back  in 
the  stoppered  bottle  "  (Langley). 

11.  Bora.v-ca)')7une.—D\ssolve  4  grammes  borax  and  3  grammes  carmine 
in  100  cubic  centimeti-es  of  warm  water.  After  three  days  add  100  cubic 
centimetres  of  70  per  cent,  alcohol,  let  stand  two  days  and  filter.  This 
solution  im])roves  on  keeping.     It  is  useful  for  staining  in  bulk. 

After  staining  with  borax-carmine,  the  tissue  should  be  placed  in  70  per 


APPENDIX.  495 

cent,  alcohol   coiitaiuini;'  T)   drops   of   hvdrocliloric  acid   to    100  cubic  centi- 
metres. 

12.  Aniline  dyes. — These  are  used  either  in  aqueous  solution  (which  may 
contain  O'Ol  per  cent,  of  caustic  potash)  or  in  water  shaken  up  with  aniline 
oil,  and  it  is  usual  to  overstain  a  tissue  with  them,  and  subsequently  to 
decolorise  with  absolute  alcohol  containing  \  its  bulk  of  aniline  oil  (from 
which  the  sections  can  pass  directly  into  xylol)  or  with  acid-alcohol  (1  to 
10  per  1000  hydrochloric  acid)  followed  by  absolute  alcohol  and  this  by 
xylol.  Those  most  employed  are  the  "  basic  "  dyes — methyl-blue,  methylene- 
blue,  gentian-violet,  toluidin-blue,  thionin,  saffranin,  and  vesuvin  ;  and  the 
"acid"  dyes — eosin,  erythrosin,  acid  magenta  or  acid  fuchsin,  and  orange  G. 
A  double  stain  is  obtained  by  combining  eosin  with  methylene  blue  or 
toluidin  blue,  the  sections  being  first  stained  for  ten  minutes  in  I  per  cent, 
aqueous  eosin  and  then,  after  rinsing  with  water,  for  twenty  minutes  in 
1  per  cent,  of  the  blue  solution,  after  which  they  are  decolorised  by  absolute 
alcohol  or  absolute  alcohol  and  aniline  oil.  The  decolorisation  is  arrested 
by  xylol.  Other  good  double  stains  are  the  eosin-methyl  blue  mixture 
devised  by  G.  Mann '  and  Jenner's  stain,  which  is  made  by  dissolving 
in  pm-e  methyl  alcohol  the  precipitate  which  is  produced  w^hen  eosin 
solution  is  added  to  methylene  blue  solution.  Jenner's  stain  is  valuable 
for  blood  films.  For  the  same  purpose  Ehrlich's  triple  stain  is  also  used. 
This  is  formed  by  mixing  together  aqueous  solution  of  orange  G.,  acid- 
fuchsin,  and  methyl-green  in  certain  proportions.- 

13.  Eosin. — A  1  per  cent,  solution  in  water  may  be  used.  The  sections 
are  first  stained  deeply  with  lipematoxylin  and  rinsed  with  water.  They  are 
then  stained  with  the  eosin  solution,  passed  through  75  per  cent,  alcohol, 
and  then  through  strong  spirit — which  is  allowed  to  dissolve  out  some 
but  not  all  of  the  eosin  stain — into  clove-oil  :  tliey  are  finally  mounted  in 
xylol  balsam  or  dammar. 

Eosin  stains  hajmogiobin  of  an  orange  red  colour  ;  so  that  the  blood 
corpuscles  are  well  shown  by  it  when  fixing  fluids  have  been  employed 
which  do  not  remove  the  haemoglobin  from  them  (such  as  mercuric  chloride, 
bichromate  of  potassium,  and  formol. 

14.  Muir's  method  of  douhle-stainiiig  ivith  eosin  and  methylene  blue. — For 
staining  haemoglobin  and  oxyphil  granules  in  cells  the  method  devised  by 
Richard  Muir  will  be  found  valuable.  It  consists  in  staining  the  sections  of 
formol-hardened  tissue  (which  are  fixed  on  a  slide)  with  saturated  solution 
of  alcohol-soluble  eosin  crystals  dissolved  in  rectified  spirit.  This  solution  is 
poured  over  the  section.s,  and  evaporated  over  a  flame  until  the  alcohol  is 
driven  off,  leaving  only  a  watery  solution.  Rinse  with  water,  place  in 
saturated  solution  of  potash  alum  for  three  minutes,  and  wash  again. 
Decolorise  with  alcohol  rendered  very  faintly  cdkaline  with  ammonia.  Wash. 
Stain  with  saturated  water-solution  of  methylene  blue  ;  wash  with  water; 
dehydrate  and  mount  in  usual  way. 

15.  Acid  fxichsin. — A  1  per  cent,  solution  in  50  per  cent,  alcohol  (to  which 

>  See  Methods  of  PhiisioJogical  Histology,  p.  216. 
-  It  is  best  to  purchase  this  solution  ready-made. 


496  THE   ESSENTIALS   OF   HISTOLOGr. 

1  drop  of  1  per  cent,  alcohol-solution  of  gentian-violet  may  be  added 
per  cubic  centimetre),  is  an  excellent  stain  for  connective  tissue  (see  p.  67). 
It  may  also  advantageously  be  used  for  developing  bone  and  tooth  and 
for  lymph-glands.  The  piece  of  tissue  is  left  for  several  days  in  a  1  per 
cent,  solution  in  95  per  cent,  alcohol  and  is  then  placed  direct  in  a  small 
quantity  of  clove-oil  for  a  few  hours,  after  which  it  is  transferred  to  molten 
paraffin. 

16.  Orcein. —DissoWe  1  gi'amme  orcein  in  100  c.c.  absolute  alcohol  con- 
taining 1  c.c.  hydrochloric  acid.  Place  the  sections  in  some  of  this  solution 
in  a  watch-glass  and  warm  slightly,  allowing  the  fluid  to  nearly  evaporate 
to  dryness.  Dehydrate  in  alcohol,  which  removes  the  excess  of  stain  ;  pass 
through  xylol  into  dammar.     Orcein  stains  especially  the  elastic  fibres. 

17.  Flemming's  method  for  karyokinetie  nuclei. — This  is  especially  valuable 
for  staining  cell-nuclei  in  mitosis.  The  tissue  having  been  appropriately 
fixed,  small  shreds  or  thin  sections  are  placed  for  two  days  in  saturated 
alcoholic  solution  of  saffranin,  mixed  with  an  equal  amount  of  aniline- 
water.  They  are  then  washed  with  distilled  water  and  decolorised 
in  aniline-alcohol  or  in  alcohol  containing  1  per  1000  hydrochloric  acid 
until  the  colour  is  washed  out  from  everything  except  the  nuclei.  They 
are  then  again  rinsed  in  water  and  placed  in  saturated  aqueous  solution 
of  gentian-violet  for  two  hours,  washed  again  in  distilled  water,  decolorised 
with  aniline-alcohol  until  only  the  nuclei  are  left  stained,  then  transferred 
to  berganiot  oil  or  xylol,  and  from  this  are  mounted  in  xylol  balsam  or 
dammar.  Gentian-violet  and  several  other  aniline  colours  may  be  employed 
in  place  of  saff'ianin  from  the  first.  Delafield's  hsmatoxjdin  (followed  by 
acid),  or  Ehrlich's  h^ematoxylin  also  stain  the  mitotic  figures  well. 

18.  Staining  with  nitrate  of  silver  (Recklinghausen). — Wash  the  fresh  tissue 
with  distilled  water  ;  immerse  in  ^  to  1  per  cent,  nitrate  of  silver  solution 
for  from  one  to  five  minutes  ;  rinse  with  distilled  water  and  expose  to 
bright  sunlight  either  in  water,  70  per  cent,  alcohol,  or  glycerine.  The 
tissue,  which  is  generally  a  thin  membrane,  may  either  be  mounted  in 
glycerine,  or  it  may  be  spread  out  flat  in  water  on  a  slide,  the  water 
draiued  off,  the  tissue  allowed  to  dry  completely,  and  then  dammar 
added.  This  method  is  used  to  exhibit  endothelium,  and  generally  to  stain 
intercellular  substance.  It  depends  upon  the  fact  that  the  chlorides  of  the 
tissues  are  almost  exclusively  confined  to  the  intercellular  sub.stance. 

The  following  methods  are  esjiecially  useful  in  investigations  relating  to 
the  nervous  system  : 

19.  Marchi's  solution. — This  is  a  mixture  of  Miillers  fluid  (2  parts)  with 
1  per  cent,  osmic  acid  (1  part).  It  is  of  value  for  staining  nerve-fibres  in 
the  earlier  stages  of  degeneration,  before  sclerosis  sets  in  (especially  a  few 
days  after  the  establishment  of  a  lesion).  All  the  degenerated  medullated 
fibres  are  stained  black,  whilst  the  rest  of  the  section  remains  almost 
unstained.  It  is  best  to  put  thin  pieces  of  the  brain  or  cord  to  be  investi- 
gated singly  into  a  large  quantity  of  the  solution  (after  previously  hardening 
for  ten  days  in  MUllei-'s  fluid),  and  to  leave  them  in  it  for  a  week  or  more  ; 
but  if  necessary   sections  can  be  stained  ;   in  tins  case  the  process  is  more 


APPENDIX.  497 

complicated.'     In  either  case  they  are  fixed  on  a  slide  and  mounted  by  the 
usual  process  in  xylol  balsam  or  dammar. 

20.  Weigert-Pal  method. — This  method  is  chiefly  used  for  the  central 
nervous  system.  By  it  all  medullated  nerve-fibres  are  stained  dark,  while 
the  grey  matter  and  any  sclero.sed  tracts  of  white  matter  are  left  uncolnured. 
The  following  modification  of  the  original  method  can  be  recommended  : 
Pieces  which  have  been  hardened  in  Miiller's  fluid  and  afterwards  kept 
a  short  time  in  alcohol  (without  washing  in  water)  are  embedded  in  cel- 
loidin,  and  sections  are  cut  as  thin  as  possible.  Or  sections  may  be  made 
by  the  freezing  method  direct  from  Miiller's  fluid,  if  the  tissue  is  first 
soaked  in  gum-water  for  a  few  hours.  In  either  case  they  are  placed  in 
water,  and  from  this  are  transferred  to  Marchi's  fluid  (see  above,  §  19), 
in  which  they  are  left  for  a  few  hours.  They  are  then  again  washed  in 
water  and  transferred  to  Kulschitzky's  hsematoxylin  (see  above,  §  3).  In 
this  they  are  left  overnight,  by  which  time  they  will  be  completely  black. 
After  again  washing  in  water  they  are  ready  to  be  bleached.  This  is 
accomplished  by  Pal's  method  as  follows  :  Place  the  overstained  sections, 
first  in  J  per  cent,  solution  of  potassium  permanganate  for  five  minutes  (or 
for  a  longer  time  in  a  weaker  solution)  ;  rinse  with  water  and  transfer  to 
Pal's  solution  (sulphite  of  soda  1  gramme,  oxalic  acid  1  gramme,  distilled 
water  200  cubic  centimetres),  in  which  the  actual  bleaching  takes  place.^ 
They  are  usually  sufiiciently  diff"erentiated  in  a  few  minutes:  if  not,  they 
can  be  left  longer  in  the  solution  without  detriment.  If  after  half  an  hour 
they  are  not  differentiated  enough,  they  must  be  put  again  (after  washing) 
into  the  permanganate  for  some  minutes,  and  then  again  into  Pal's  solution. 
After  difi'erentiation  they  are  passed  through  water,  alcohol  (with  or  without 
eosin),  and  oil  of  bergamot  (or  xylol),  to  be  mounted  in  xylol  balsam  or 
dammar.  The  advantages  which  this  modification  has  over  the  original 
method  are  (1)  even  the  finest  medullated  fibres  are  brought  to  view  with 
great  surety  ;  (2)  the  staining  of  the  fibres  is  jet  black,  and  offers  a  strong 
contrast  to  the  colourless  grey  matter  ;  (3)  the  sections  are  easily  seen  and 
lifted  out  of  the  acid  hsematoxylin,  which  has  very  little  colour  ;  (4)  it  is 
diflScult  to  overbleach  the  sections ;  (5)  the  stain  is  remarkably  per- 
manent. 

Asa  modification  of  the  above,  Bolton  recommends  to  harden  with  formol, 
place  the  sections  for  a  few  minutes  in  1  per  cent,  osmic  acid,  stain  for 
two  hours  in  Kulschitzky's  hsematoxylin  at  40°  C,  and  then  proceed  with 
the  bleaching  process. 

21.  Staining  loith  chloride  of  gold. — a.  Cohnheim's  method. — Place  the  fresh 
tissue  for  from  thirty  to  sixty  minutes  in  a  i  per  cent,  solution  of  chloride 
of  gold  ;  then  wash  and  transfer  to  a  large  quantity  of  water  faintly  acidu-, 
lated  with  acetic  acid.  Keep  for  two  or  three  days  in  the  bght  in  a  warm 
place.  This  answers  very  well  for  the  cornea.  If  it  be  principally  desired 
to  stain  the  nerve-fibrils  within  the  epithelium,  the  cornea  may  be  trans- 
ferred after  twenty-four  hours  (the  outlines  of  the  larger  nerves  should  be 

1  See  Hamilton,  Brain,  1897,  p.  180. 

2  Diluted  sulphurous  acid  solution  may  be  employed  instead  of  Pal's  solution. 

2l 


498  THE   ESSENTIALS   OF   HISTOLOGY. 

just  apparent  to  the  naked  eye)  to  a  mixture  of  glycerine  (1  part)  and  water 
(2  parts),  and  left  in  this  for  twenty-four  hours  raore  (Klein). 

/?.  Loicifs  method. — Place  small  pieces  of  the  fresh  tissue  iu  a  mixture  of 
1  part  of  formic  acid  to  2  to  4  parts  of  water  for  one- half  to  one  minute  ; 
then  in  1  per  cent,  chloride  of  gold  solution  for  ten  to  fifteen  minutes  ;  then 
back  again  into  the  formic  acid  mixture  for  twenty-four  hours,  and  into 
pure  formic  acid  for  twenty-four  hours  more.  After  removal  from  the  gold, 
and  whilst  in  the  acid,  the  tissue  must  be  kept  in  the  dark.  This  method  is 
especially  good  for  motor  nerve  endings  iu  skeletal  muscle. 

y.  Rayiviei^s  method. — Immerse  in  lemon-juice  for  five  to  ten  minutes, 
then  wash  with  water  and  jilace  in  1  per  cent,  gold-chloride  solution  for 
twenty  minutes.  Then  treat  either  as  in  Cohnheim's  or  as  in  Lowit's 
method. 

22.  Golgi's  ehromate  of  silver  methods. — These  are  chiefly  employed  for 
investigating  the  relations  of  cells  and  fibres  in  the  central  nervous  system. 
Two  methods  are  mostly  used,  as  follows  : 

a.  Very  small  pieces  of  the  tissue  which  has  been  hardened  for  some 
weeks  in  3  per  cent,  bichromate  of  potassium  or  Miiller's  fluid  are  placed  for 
half  an  hour  in  the  dark  in  075  per  cent,  nitrate  of  silver  solution,  and 
are  then  transferred  for  twenty-four  hours  or  more  to  a  fresh  quantity 
of  the  same  solution  (to  which  a  trace  of  formic  acid  may  be  added).  They 
may  then  be  placed  in  96  per  cent,  alcohol  (half  an  hour),  and  sections, 
which  need  not  be  thin,  are  cut  either  from  celloidin  with  a  microtome 
or  with  the  free  hand  after  embedding  (but  not  soaking)  with  parafliu. 
The  sections  are  mounted  in  xylol  balsam,  which  is  allowed  to  dry  on  the 
slide  :  they  must  not  be  covered  with  a  cover-glass,  but  the  balsam  must 
remain  exposed  to  the  air. 

/3.  Instead  of  being  slowly  hardened  in  bichromate,  the  tissue  is  placed 
at  once  in  very  small  pieces  in  a  mixture  of  bichromate  and  osmic  (3  parts 
of  3  per  cent,  bichromate  of  potash  or  of  Miillers  fluid  to  1  of  osmic  acid). 
In  this  it  remains  from  one  to  eight  days,  a  piece  being  transferred  each 
day  to  0'75  per  cent,  silver  nitrate.  The  subsequent  procedure  is  the  same 
aa  described  under  a.  For  some  organs  it  is  found  advantageous  to  repeat 
the  process,  replacing  them  for  a  day  or  two  in  the  osmic-bichromate 
mixture  after  silver  nitrate  and  then  putting  them  back  into  silver  nitrate 
(Cajal's  double  method).  This  method  is  not  only  more  rapid  than  that  in 
which  bichi'omate  of  potassium  alone  is  used,  but  is  more  sure  in  its  results. 

23.  Ehrlich's  methylene-blue  method. — This  method  is  one  of  great  value 
for  exhibiting  nerve-terminations,  and  in  some  cases  the  relations  of  nerve- 
cells  and  fibres  in  the  central  nervous  system.  For  its  application  the 
tissue  must  be  living  :  it  is  therefore  best  applied  by  injecting  a  solution 
of  methylene-blue  (1  part  to  100  of  warm  saline  solution)  into  a  vein  in 
an  anaesthetised  mammal,  until  the  whole  blood  is  of  a  bluish  colour  ;  or 
the  injection  may  be  made  through  the  vessels  of  the  part  to  be  investi- 
gated, immediately  after  killing  an  animal.  But  fairly  good  results  can 
also  be  obtained  by  immersing  small  pieces  of  freshly-excised  living  tissue 
in  a  less  concentrated  solution  (0"1  -pQV  cent.),  or,  in  the  case  of  the  central 


APPENDIX.  499 

nervous  syetem,  by  dusting  the  raethylene-blue  powder  over  a  freshly-cut 
surface,  allowing  some  time  for  it  to  penetrate,  and  then  treating  it  with 
picrate  of  ammonia  and  Bethe's  solution.  In  either  case  the  tissue  should 
be  freely  exposed  to  air;  the  blue  colour  then  appears  in  the  nerve- 
cells  and  axis-cylinders,  even  to  their  finest  ramifications.  It  does  not 
however  remain,  but  after  a  time  fades  from  them  while  other  tissues 
become  coloured.  To  fix  the  stain  the  tissue  is  taken  at  the  moment  that 
the  nerve-fibres  are  most  distinctly  seen  and  is  placed  for  an  hour  or  two 
in  saturated  solution  of  picrate  of  ammonia,  after  which  the  preparation 
can  be  mounted  in  glycerine  containing  picrate  of  ammonia.  But  to  allow 
of  sections  being  made  from  it  for  mounting  in  balsam  or  dammar,  it  must, 
subsequently  to  the  treatment  with  picrate  of  ammonia,  be  placed  for  some 
hours  in  Bethe's  fluid,  viz.  : 

Molybdate  of  ammonia, 1  gramme. 

Chromic  acid  2  per  cent,   solution,    -         -         -         -  10  c.c. 

Distilled  water, 10  c.c. 

Hydrochloric  acid,      --.-.--  1  drop. 

This  renders  the  colour  insoluble  in  alcohol. 

24.  Sihler's  method  of  stainmg  nerve-endings  in  muscle  and  blood-vessels. — 
Macerate  the  tissue  for  eighteen  hours  in  the  following  solution  : 

Ordinary  acetic  acid, -         1  part. 

Glycerine, 1  part. 

1  per  cent,   chloral  hydrate  solution,      .         -         -         -         ti  parts. 

From  this  transfer  to  glycerine  for  from  one  to  two  hours  ;  then  unravel 
somewhat  with  needles  and  place  for  from  three  to  ten  days  in  the 
following  : 

Ehrlich's  hsematoxylin,    - 1  part. 

Glycerine, -         .         1  part. 

I  per  cent,   chloral  hydrate  solution,      ...         -         6  parts. 

It  may  then  be  kept  for  any  desired  time  in  glycerine,  which  should  be 
changed  several  times. 

Preparations  are  made  by  careful  dissociation  with  needles.  If  over- 
stained  they  may  be  differentiated  by  acetic  acid  until  the  dark-blue  colour 
is  changed  to  violet.  The  muscle  spindles  and  the  end-plates  are  well 
shown  by  this  method. 

25.  Nissl's  method  of  staining  the  chromatic  granules  in  nerve-cells. — This 
is  a  method  of  overstaining  with  methylene  blue  and  subsequent  differ- 
entiation with  alcohol  (see  §  12).  Nissl  recommended  90  per  cent,  alcohol 
as  the  hardening  agent,  but  both  formol  and  corrosive  sublimate  followed 
by  alcohol  may  be  employed  also.  Toluidin-blue  (Mann)  may  be  used  in 
place  of  methylene-blue.  The  sections  may  first  be  stained  with  1  per  cent, 
aqueous  solution  of  eosin,  and  then,  after  rinsing  in  water,  with  1  per 
cent,  methylene-blue  solution  :  they  are  best  differentiated  in  aniline-alcohol. 
The  effect  of  heating  the  solutions  to  about  70°  C.  is  to  accelerate  and 
accentuate  the  staining,  which  will  then  take  only  a  few  minutes, 

2i2 


500  THE   ESSENTIALS   OF   HISTOLOGY. 

A  Nissl ,  stain  may  also  be  obtained  by  placing  thin  pieces  of  the  fixed 
and  hardened. nervous  tissue  in  1  per  cent,  solution  of  thionin  for  several 
days  ;  after  which  the  tissue  is  dehydrated  and  embedded  in  paraffin. 

26.  CajaVs  reduced  silver  method  for  exhibiting  netirofibrih  within  nerve-cells 
and  -fibres. — A  small  piece  of  the  tissue  (brain,  spinal  cord,  ganglion,  etc.), 
not  more  than  4  mm.  thick,  and  preferably  from  a  young  animal,  is  placed 
in  50  CO.  of  rectified  spirit  to  which  5  drops  of  ammonia  are  added.  After 
twenty-four  hours  in  this,  rinse  with  distilled  water  and  place  in  a  large 
quantity  of  1  per  cent.- solution  of  silver  nitrate,  which  is  maintained  at  a 
temperature  of  about  30°  C.  After  being  five  or  six  days  in  this  solution, 
the  piece  is  removed,  mixed  for  a  few  seconds  in  distilled  water,  and 
transferred  for  twenty-four  hours  to  the  following  solution  : 

Hydrokinone  (or  pyrogallic  acid),  -         -         -         -  1  to  1*5  grammes. 

Distilled  water, 100  cub.  cent. 

Formol, 5  to  10  cub.  cent. 

Rectified  spirit, 10  to  15  cub.  cent. 

The  addition  of  alcohol  to  the  above  is  not  indispensable,  but  favours 
penetration.  The  piece  is  then  washed  in  water  for  some  minutes,  trans- 
ferred to  alcohol,  embedded  in  celloidin,  and  sections  are  prepared  and 
mounted  in  the  ordinary  way. 


INDEX. 


601 


INDEX. 


ACH 

Achromatic  spindle,  7,  31. 

Achromatic  substance,  8. 

Adenoid  tissue,  76. 

Adipose  tissue,  73. 

Adrenals,     See  suprarenal  capsules. 

Air-bubbles,  27. 

Ameloblasts,  271. 

Amreba,  3. 

Angioblasts,  196. 

Ansa  lenticularis,  415. 

Aorta,  structure  of,  189. 

Appendix,  •IS-i.    (See  also  verniiforni.) 

Archoplasni,  8. 

Areolar  tissue,  68. 

cells  of,  70. 

fibres  of,  68. 

Arrector  pili,  243. 
Arteries,  nerves  of,  196. 

—  structure  of,  184. 

—  variation  in  structure  of,  189. 

—  and  veins,  smaller,  structure  of,  192. 
Articular  cartilage,  87. 

—  corpuscles,  169. 
Attraction  sphere,  7. 
Auerbach,  plexus  of,  296. 
Autonomic  nerves,  132. 
Axon,  138,  143. 

Bacteria,  27. 
Baillarger,  lines  of,  428. 
Basilar  membrane,  479. 
Basement  membranes,  77. 
Bechterew,  nucleus  of.     See  nucleus. 
Bellini,  ducts  of,  324. 
Bile-ducts,  313. 
Bladder,  329. 
Blastoderm,  22. 

Blood-corpuscles,   action  of   reagents 
upon,  41,  44. 

—  of  amphibia,  45. 

—  coloured,  31,  32,  41. 

—  colourless,  32. 

amoeboid  phenomena  of,  48. 

granules  of,  33. 

migration    from    blood-vessels, 

51,  72. 
varieties  of,  33. 

—  development  of,  36,  40. 

—  enumeration  of,  30. 

—  structure  of,  31. 


CEL 

Blood-crystals,  43. 
Blood-film,  28. 
Blood-platelets,  35,  47. 
Blood-vessels,  development  of,  36,  196. 

—  structure  of,  184,  192. 
Bone,  96. 

—  development  of,  101. 

—  lacuna;  and  canaliculi  of,  98. 

—  lamella  of,  98. 

—  marrow  of,  38. 

Bowman,  glands  of.     See  glands. 

—  membrane  of,  447. 
Bronchi,  255. 
Bronchial  tubes,  257. 

Brain.  See  cerebrum,  cerebellum, 
medulla  oblongata,  mesenceph- 
alon, pons  Varolii. 

—  divisions  of,  374. 

—  membranes  of,  441. 
Brunner,  glands  of.     See  glands. 
Burdach,  tract  of.     See  tracts. 
Bundle.     See  tracts. 

Calleja,  islands  of,  396. 
Capillaries,  193. 

—  circulation  in,  194, 
Carotid  gland,  222. 
Cartilage,  86. 

—  articular,  87. 

—  costal,  87,  92. 

—  development  of,  90. 

—  embrj'onic,  90. 

—  hyaline,  87. 

—  ossification  of,  101. 

—  parenchymatous,  90. 

—  transitional,  88. 

—  varieties  of,  86. 
Cartilage-cells,  87. 

—  capsules  of,  88. 

Cajal's    method    of    staining    neuro- 
fibrils, 499. 
Celloidin  for  embedding,  487. 
Cell-plate,  16. 
Cells,  division  of,  10. 

amitotic,  10. 

reduction,  14. 

—  embryonic,  1. 

—  membrane  of,  8. 

—  nucleus  of,  8. 

—  structure  of,  2. 


502 


INDEX. 


CEM 


FIB 


Cement.     See  crusta  petrosa. 
Central  fovea  of  retina,  463. 

—  tendon  of  diaphragm,  191. 
Centriole,  7. 
Centrosome,  7. 
Cerebellum,  417. 

—  peduncles  of,  398,  402,  424. 

superior,  398,  411,  424. 

inferior.     See  restiform  body. 

middle,  390,  424. 

Cerebrum,  424. 

—  basal  ganglia  of,  440. 

—  cortex  of,  424. 

—  —  structure  of  different  parts,  432. 

—  peduncle  of,  405. 
Chondrin-balls,  90. 
Choroid  coat  of  eye,  451. 
Chromatic  substance,  8. 
Chromatolysis,  140.  [224. 
Chromaffin  or  chromophil  cells,  221, 
Chromosomes,  9,  12. 

Cilia,  64. 

—  action  of,  65. 

theories  regarding,  66. 

Ciliary  muscle,  452. 

Clarke,  column  of,  370. 

Claustrum,  426. 

Coccygeal  gland.     See  glands. 

Cochlea,  474. 

Cohnheim,  areas  of,  112. 

—  method  of  staining  nerve-endings, 

497. 
Collaterals,  148. 
Colostrum-corpuscles,  248. 
Comma  tract,     ^ee  tracts. 
Commissures   of   cerebrum,   anterior, 

439. 
posterior,  410. 

—  of  spinal  cord,  356. 
Conjunctiva,  444. 
Connective  tissue,  cells  of,  70. 

development  of,  82. 

fibres  of,  68. 

jelly-like,  77. 

—  tissues,  68. 
Cornea,  447. 

—  nerve  endings  in,  176,  449. 
Corpora  albicantia  {mammillaria),414. 

—  geniculata,  412. 

—  quadrigemina,  406. 
Corpus  luteum,  350. 

—  striatum,  440. 

—  subthalamicum,  415. 
Corti,  organ  of,  479. 
Cotton  fibres,  27. 

Cowper,  glands  of.     See  glands. 
Crusta,  405. 

—  petrosa,  269. 
Cutis  vera,  230. 
Cytomitome,  7. 
Cytoplasm,  2. 


Deiteks,  cells  of,  481. 

—  nucleus  of.     See  nucleus. 
Dendrons,  138. 

Dentine,  263. 

—  formation  of,  272. 
Descemet,  membrane  of,  449. 
Deutoplasm,  5. 

Dilatator  pupillaj,  454. 
Dobie,  line  of,  1 13. 
Doyere,  eminence  of,  182. 
Dust,  27. 

Ear,  469. 

Ebner,  glands  of.     See  glands. 

Ehrlich's  methjdene-blue  method,  498. 

Elastic  tissue,  79. 

Eleideu,  228. 

Embedding,  methods  of,  486. 

Enamel,  263. 

—  formation  of,  271. 

—  organ,  272. 
End-bulbs,  168. 
Endocardium,  252. 
Endomysium,  115. 
Kndoneurium,  135. 
Endoplasm,  5. 
Endotheliu!)!.  55. 
End-plates,  180. 
Ependyma,  373,  389. 
Epicardium,  252. 
Epidermis,  226. 
Epididymis,  334. 
Epineurium,  134. 

Epiphysis  cerebri.     See  pineal  gland. 
Epithelium,  52. 

—  ciliated,  55,  64. 

—  classification  of,  53. 

—  columnar,  55,  61. 

—  glandular,  56. 

—  nerve  endings  in,  174. 

—  pavement.  55. 

—  stratified,  54. 

—  transitional,  55. 
Epitrichial  layer,  229. 
Erectile  tissue,  330. 
Erythroblasts,  36. 
Erythrocytes.     See    blood-corpuscles, 

coloured. 
Eustachian  tube,  470. 
Exoplasm,  5. 
Eye,  443. 
Eyelids,  444. 
Eye-piece,  24. 

Fallopian  tubes,  351. 
Fat.     See  adipose  tissue. 

—  absorption  of,  304. 

—  in  cartilage  cells,  90,  92. 
Fenestrated  membrane,  187. 
Fibres.    See  connective  tissue,  muscle, 

nerve,  etc. 
Fibrin,  35. 


INDEX. 


503 


KIB 

Fibro-cartilcige,  elastic,  9.S. 

—  white,  93. 
Fibrous  tissue,  80. 
Fillet.     See  tract  of  tillet. 
Fimbria,  434.    ■ 
Flechsig,  method  of,  360. 

—  tract  of.     See  tracts. 
Flemming, germ-cent  reof,20o,201),216. 

—  stainable  bodies  of,  'JOi),  216. 

—  method  of  staining  nuclei,  4Sn. 
Forel,  decussation  of,  4U3  (footnote). 
Freezing  method    for   preparation  of 

sections,  487. 

GAr.L-lSL.VDDKK,   'M4. 

Ganglia,  138. 

—  cells  of,  14<». 

—  development  of,  162. 
Ganglion  of  cochlea,  38.5. 

of  glossopharyngeal,  384. 

Scarpa,  SSo. 

—  —  of  vagus,  383. 

—  Gasserian,  395. 

—  geniculate,  393. 

—  of  habenula,  405,  414. 

—  interpeduncular,  405. 
Gas-chamber,  60. 
Genital  corpuscles,  169. 
Gennari,  line  of,  428. 
Germ-centre,  205,  209,  216. 
Germ-nuclei,  18. 
Gianuzzi,  crescents  of,  283. 
Gland  or  glands. 

—  agminated,  209,  300. 

—  anal,  308. 

—  of  Bowman,  469. 

—  of  Brunner,  294,  3(il. 

—  carotid,  222. 

—  ceruminous,  245,  469. 

—  classification  of,  56. 

—  coccygeal,  222. 

—  of  Cowper,  331. 

—  ductless,  59. 

—  of  Ebner,  276. 

—  gastric,  288. 

—  haemal,  207. 

—  internallj'  secreting,  59. 

—  lacrymal,  446. 

—  of  Lieberkiihn,  279. 

—  of  Littre,  331. 

—  lymph,  203. 

—  mammary,  246. 

—  Meibomian,  445. 

—  Pacchionian,  442. 

—  pineal,  415. 

—  pituitary,  224 

—  racemose,  58. 

—  saccular,  58. 

—  salivarj',  281. 

—  sebaceous,  243. 

—  secreting,  56. 


HEN 

Gland  or  glands,    secreting,  varieties 
of,  58. 

—  serous,  276. 

—  solitary,  209,  299. 

—  sweat,  244. 

—  thymus,  210. 

—  tubular,  58. 
(ilisson,  i:apsule  of,  311. 
(Jlomeruli  of  kidney,  320. 

—  olfactory,  439. 

Glycogen     in     colourless     blood-cor- 
puscles, 47. 

—  in  liver  cells,  313. 
Goblet-cells,  63. 

Gold-methods     of     staining      nerve- 
endings,  497,  498. 
Golgi,  organs  of,  174. 

—  cells  of,  418. 

—  methods  of  preparing  the  nervous 

system,  498. 

—  reticulum  of,  141,  142. 

—  types  of  nerve-cells,  148. 
GoU,  tract  of.     6'ee  tracts. 
Gowers,  tract  of.     See  tracts. 
Graafian  follicles,  345. 
Grandry,  corpuscles  of,  169. 
Grannies  of  protoplasm,  4. 

—  of  colourless  blood-corpuscles,  33. 
Ground-substance  of  connective  tissue, 

2,  68. 
Gudden,  atrophy  of,  158. 

—  bundle  of.     See  tracts. 

—  commissure  of,  410. 
Gullet.     See  oesophagus. 
Gustatory  cells,  278. 

—  pore,  278. 

H.tMAL  glands.     See  glands. 

Hpematoidin,  44. 

Hctmin,  44. 

Ha;moglobin,  43. 

Hsemolysis,  42. 

Hair-cells  of  internal  ear,  473, 480, 481 . 

Hair-follicle,  structure  of,  235. 

Hairs,  27,  234. 

—  development  of,  241. 

—  muscles  of,  243. 

Hassal,  concentric  corpuscles  of,  211. 
Haversian  canals,  98. 

—  systems,  99. 

Haycraft,  views  of,  on  muscle  struc- 
ture, 113. 
Heart,  250. 

—  muscle  of,  123. 

—  nerves  of,  253. 

—  valves  of,  253. 

Helweg,  bundle  of.     See  tracts. 
Henle,  fenestrated  membrane  of,  187. 

—  looped  tubules  of,  324. 

—  sheath  of,  136. 
Hensen,  line  of,  113. 


^04 


INDEX. 


HEP 

Hepatic  lobules,  310. 

—  cells,  312. 

Herbst,  corpuscles  of,  173. 
Hippocampus  major,  434. 
His,  bundle  of,  252. 
Histogenesis,  20. 
Histologj',  meaning  of  term,  1. 
Hyaloplasm,  4. 

Hj'pophysis    cerebri.      See    pituitary 
body. 

Idiozome,  342. 
Internal  capsule,  440. 
Intestine,  large,  308. 

—  small,  296. 
Iris,  453. 

Jelly  of  Wharton,  85. 

Karyokine.sis,  10. 
Kei'ato-hj'aline,  229. 
Kidaey,  320. 

—  bldod-vessels  of,  32(i. 
Krause,  membi'ane  of,  113,  116. 

Labyrinth  of  ear,  472. 

of  kidney,  325. 
Lacteals,  304. 
Langerhans,  islets  of,  316. 

—  centro-acinar  cells  of,  318. 
Lanugo,  242. 

Larjnx,  256. 

Lens,  465. 

Leucocytes.       {Set    blood-corpuscles, 

colourless). 
Lieberkiihn,  crypts  of,  297. 
Linen  fibres,  27. 

Lissauer,  bundle  of.     See  tracts. 
Littre,  glands  of.     See  glands. 
Liver,  310. 

—  blood-vessels  of,  198,  311. 

—  cells  of,  257. 

—  ducts  of,  313. 

—  lobules  of,  310. 

—  lymphatics  of,  315. 
Loewenthal,  tract  of.     See  tracts. 
Lung,  256. 

—  alveoli  of,  261. 

—  blood-vessels  of,  261. 

—  Ijmph-vessels  of,  262. 
Lymph-glands   or   lymphatic  glands, 

203. 

haemal,  206. 

Lymph-vessels  or  lymphatics,  198. 

—  connection  with  cells  of  connective 

tissue,  73,  201. 

—  development  of,  201. 

—  nerves  of,  20<J. 

Lymph-corpuscles.         See    blood-cor- 
puscles, colourless. 

Lymphocytes,  34. 


MUS 

Lymphoid  tissue,  76,  209. 

—  —  development  of,  209. 

Macula  lutea  of  retina,  463. 
Malpighi,  rete  mucosnm  of,  227. 

—  pyramids  of,  320. 

Malpighian  corpuscles  of  kidney,  320. 

of  spleen,  2u9,  214. 

Mammary  glands,  246. 
Marchi's  method  of   staining  degen- 
erated nerve-fibres,  496. 
Marrow,  38. 
Measuring  objects,  25. 
Medulla  oblongata,  374. 
Megakaryocytes,  40,  218. 
Meissuer,  plexus  of,  297. 
Membrana  tectoria,  482. 

—  tympani,  469. 
Mesencephalon,  401. 
Mesothelium,  55. 
Methods  of  embedding,  486. 

—  of  measuring  microscopic  objects, 

25, 

—  of  mounting  sections,  491. 

—  of  preparing  sections,  486. 

—  of  preserving  and  hardening,  484. 

—  of  staining,  492. 

Meynert,  bundle  of.     See  tracts. 

—  decussation  of,  403,  409. 
Micrometer,  25. 
Microscope,  24. 

Microscopic  work,  requisites  for,  24. 
Microtomes,  487. 

Migration  of  colourless  blood-corpus- 
cles, 51,  195. 
Mitochondria,  5. 
Mitosis,  10. 
Moist  chamber,  61. 
Mouakow,  bundle  of.     See  tracts. 
Mould,  27. 

Mounting  solutions,  484. 
Mucus-secreting  cells,  63. 
Mliller,  fibres  of,  462. 

—  helicine  arteries  of,  330. 

—  muscle  of,  453. 

Muscle,  accessory  disks  of,  117. 

—  blood-vessels   and  lymphatics    of, 

121. 

—  cardiac,  123. 

—  changes  in  contraction,  116,  119. 

—  corpuscles,  113. 

—  development  of,  122. 

—  ending  of,  in  tendon,  120. 

—  involuntary  or  plain,  126. 

development  of,  127. 

of  arteries,  187. 

—  nerves  of,  121,  177,  180. 

—  nuclei  of,  113. 

—  of  heart,  123. 

—  of  insects,  115,  116. 

—  in  polarized  light,  118. 


INDEX. 


506 


MUS 

Muscle,  principal  disk  of,  117. 

—  red,  llo. 

—  spindles,  122,  177. 

—  structure  of,  compared  with  proto- 

plasm, 119. 

—  voluntary  or  cross-striated,  11 1. 
Myelopla.xes,  40. 
Myocardium,  250. 

Nails,  232. 

—  development  of,  234. 
Nerve-cells,  138. 

—  development  of,  161. 

—  processes  of,  138,  143. 

—  reticulum  of,  141. 

—  trophospongium  of,  143. 

—  types  of,  148. 
Nerve-fibres,  axis  cylinder  of,  132. 

—  degeneration  of,  154. 

—  ilevelopmeiit  of,  161. 

—  meduUated,  129. 

—  medullary  segments  of,  131. 

—  motor,  terminations  of,  180. 

—  non-medullated,  133. 

—  regeneration  of,  157- 

—  sensory,  modes  of  termination  of, 

166,  177. 

—  sheaths  of,  130. 

—  varieties  of,  128. 
Nerve-trunks,  structure  of,  134. 
Nervi  nervorum,  136. 
Neuroblasts,  161. 
Neurofibrils,  l;s2,  140,  177. 
Neuroglia,  159. 
Neurokeratin,  131, 
Neurolemma,  130. 

Neurone,  138. 

—  theory,  148. 
Neuro-synapse,  148. 

Nissl,  granules  of,  in  nerve-cells,  138. 
Nissl's    degeneration    of    nerve-cells, 
140,  155. 

—  method  of  staining  nerve-cells,  499. 
Nucleolus,  8. 

Nucleus  of  cell. 
Nucleus  or  nuclei. 

—  of  abducens,  394. 

—  of  accessory,  378,  381. 
"—  of  Bechterew,  389,  397. 

—  caudatus,  440. 

—  of  cochlear  nerve,  385. 

—  cuneatus,  377. 

—  of  Deiters,  388,  392,  397,  402. 

—  dentatus  cerebelli,  417- 

—  of  facial,  392. 

—  of  glossopharyngeal,  379,  384. 

—  gracilis,  377. 

—  of  hypoglossal,  378,  381. 

—  lenticularis,  440. 

—  oculomotor,  401. 

—  of  olive,  380. 


PIT 

Nucleus  or  nuclei. 

—  of  pons,  390. 

—  of   posterior   longitudinal    bundle, 

403. 
~  preolivary,  392. 

—  red,  of  tcgumentum,  402. 

—  semilunar,  392. 

—  of  Stilling,  417. 

—  superior  olivary,  392. 

—  tecti  (s.  fastigii),  417. 

—  of  thalamus,  411.  • 

—  of  trapezium,  391. 

—  of  trigeminal,  394. 

—  of  vagus,  379,  383. 

—  of  vestibular  nerve,  387. 

Objective,  24. 
Ocular,  24. 
Odontoblasts,  268. 
CEsophagus,  280. 
Olfactory  bulb,  436. 

—  cells,  439,  468. 

—  mucous  membrane,  467. 

—  path,  439. 

—  tract,  436. 
Olive,  375. 

—  superior,  392. 
Omentum,  191. 
Onychogenic  substance,  232. 
Opsonins,  50. 

Optic  chiasma,  409. 

—  nerves,  409. 

—  thalamus,  410. 

—  tract,  409. 
Ossification  in  cartilage,  102. 

—  in  membrane,  108. 
Osteoblasts,  100,  103. 
Osteoclasts,  105. 
Osteogenic  fibres,  108. 
Ovary,  314. 

Ovum,  22,  343. 

—  division  of,  17. 

Pacinian  corpuscles,  169. 
Pancreas,  316. 
Papillae  of  tongue,  275. 

—  of  skin,  230. 
Paranucleus,  5,  318. 
Paraplasm,  5. 
Parathyroids,  222. 
Penis,  330. 
Pericardium,  252. 
Perineurium,  134. 
Periosteum,  100. 

Peyer,  patches  of,  209,  300. 
Phasocytes,  33,  50,  218. 
Pharynx,  280. 
Pick,  bundle  of,  376. 
Pigment-cells,  72. 
Pineal  gland,  415. 
Pituitary  body,  224. 


506 


INDEX. 


PLE 

Pleura,  2(j2. 
Polar  bodies,  17. 
Pons  Varolii,  390. 
Portal  canal,  311. 

Posterior   longitudinal    bundle.      See 
tracts. 

—  commissure.     See  commissures. 
Prickle-cells,  54. 

Pronuclei,  18. 

Proprio-spinal  tibres  of  cord,  361,  306. 

Prostate,  331. 

Protoplasm,  2. 

Purkinje,  cells  of,  41S. 

—  fibres  of,  125,  252. 

Pyramids  of  medulla  oblongata,  375. 

Ranvier,  constrictions  of,  130. 
Recklinghausen,   method  of  staining 

with  silver  nitrate,  496. 
Reil,  fillet  of,  398. 

—  island  of,  420. 
Reissner,  membrane  of,  477. 
Remak,  fibres  of,  133. 
Restiform  body,  380,  389,  424. 
Reticular  or  retiform  tissue,  75. 
Retina,  454. 

—  macula  lutea  of,  463. 

—  pars  ciliaris  of,  465. 
Rhinencephalon,  4.33. 
Rolando,  tubercle  of,  377. 
RoUett's  method  of  staining  muscle, 

110. 

Rouleaux  (of  blood-corpuscles),  causa- 
tion of,  43. 

Ruffini,  organs  of,  173. 

Saccule,  473. 
Salivary  corpuscles,  52. 

—  glands,  281. 
Sarcolemma,  111. 
Sarcomeres,  116. 
Sarcoplasm,  112. 
Sarcostyles,  112. 
Sarcous  elements,  116. 
Schwann,  sheath  of,  130. 
Sclerotic  coat  of  eye,  446. 
Sebaceous  glands.     .SV^  glands. 
Sections,  preparation  of,  480. 
Semicircular  canals,  473. 
Seminiferous  tubules,  337. 
Serous  membranes,  201. 
Sertoli,  cells  of,  341. 
Sharpey,  fibres  of,  99,  100. 

Sihler's   method    of    staining    nerve- 
endings,  499. 
Silver-methods,  496,  499. 
Sinusoids,  185,  197. 
Skin,  226. 

Spermatogenesis,  341. 
Spermatozoa,  338. 


TRA 

Sphincter  ani,  internal,  308. 

Sphincter  piipilhe,  453. 

Spinal  bulb.     See  medulla  oblongata. 

Spinal  cord,  355. 

— •  —  blood-vessels  of,  373. 

central  canal  of,  356,  373,  378. 

characters    in    different    parts, 

.358. 

—  —  connection  of  nerve  roots  with, 

371. 

gi'ey  mattei'  of,  366. 

membranes  of,  355. 

nerve-cells  of,  366. 

— ■  —  tracts  in,  360. 

Spinal  ganglia,  149. 

Spleen,  213. 

Spongioblasts,  161. 

Spongioplasm,  4. 

Staining  of  sections,  493. 

Stanley-Kent,  bundle  of,  252. 

Starch  granules,  25. 

Stilling,  nucleus  of,  in  cord,  370. 

Stomach,  287. 

—  blood-vessels  of,  294. 

—  glands  of,  288. 

-—  lymphatics  of,  294. 
Stomata,  201. 

Stroma  (of  blood  corpuscle),  43. 
Substantia  nigra,  405. 
Subthalamus,  415. 
Suprarenal  capsules,  218. 
Sweat-glands,  244. 
Sylvian  aqueduct,  401. 
Sympathetic  ganglia,  150. 

—  nerves,  133. 
Synapse,  148. 
Syncytium,  2,  125,  194. 
Synovial  membranes,  90. 

Tactile  corpuscles,  167. 

—  disks,  169,  177. 
Taste-buds,  277. 
Teeth,  structure  of,  263. 

—  formation  of,  269. 

—  pulp  of,  268. 
Tegmentum,  402. 
Tendon,  82. 

—  nerve-endings  in,  174. 
Testicle,  332. 
Thalamencephalon,  410. 
Thalamus,  410. 
Thrombocytes,  35. 
Thymus  gland,  210. 
Thyroid  body,  221. 
Tissues,  enumeration  of,  1. 

—  formation  from  blastodermic  layers, 

22. 
Tongue,  275. 
Tonsils,  207. 
Tooth.     See  teeth. 
Trachea,  254. 


INDEX. 


507 


TUA 

Tract  or  tracts  or  bundles. 

—  anterior   longitiuiinal.     See   tecto- 

spijKil  tract. 

—  anterolateral  ascending.     See  tract 

of  Gowers. 

descending.     See  tract  of  Loew- 

enthal. 

—  bulbo  thalamic.    See  tract  of  fillet. 

—  of  Burdach,  360,  377. 

—  central,  of  cranial  nerves,  398. 

—  central,  of  tegmentum,  3S1,  397. 

—  cerebello-bulhar,  384. 

—  comma,  361. 

—  of  cord,  360. 

—  cortico-bulbar,  396,  398. 

—  cortico-spinal.  (SVe  pyramidal  tract. 

—  crossed  pyramidal.     iS'ee  pyramidal 

tract. 

—  descending  cerebellar,  399. 

—  direct  pyramidal.      See  pyramidal 

tract. 

—  of  (ioll,  360,  377. 

—  myelination  of,  360. 

—  of  fillet,  377,  387,  397,  404,  411. 

—  of  Flechsig,  365,  381. 

—  of  (iowers,  365,  381,  399. 

—  of  Gudden,  403  (footnote),  414. 

—  of  Helweg,  365. 

—  of  Lissauer,  366,  371. 

—  of  Loewenthal,  363. 

—  of  Marie,  366. 

—  of  Meynert,  405. 

—  of  Monakow,  365,  396,  403. 

—  of  Miinzer,  403. 

—  of  Pick,  376. 

—  olfactory,  436. 

—  olivo-spinal.     See  tract  of  Helweg. 

—  optic,  409. 

—  ponto-spinal,  397. 

—  posterior    longitudinal,    363,    388, 

392,  396,  402. 

—  prepyramidal.     See  tract  of  Mona- 

kow. 

—  pyramidal,  361,  376,  390,  396,  405, 

409. 

—  of  Risien-Russell,  418. 

—  rubro-spinal.     See  tract  of  Mona- 

kow. 


YEA 

Tract  or  tracts  or  bundles. 

—  spino-cerebellar,  365,  370. 

—  spino-tectal,  366. 

—  spino-thalaniic,  366. 

—  tecto-,spinal,  36.5,  .397,  403. 

—  thalamo-bulbar,  398. 

—  thalamo-olivary,  397. 

—  transverse  peduncular,  410. 

—  ventral    longitudinal.       See   tecto- 

spinal tract. 

—  vestibulo-motor.        *S^ee     posterior 

longitudinal  tract. 

—  vestibulo-spinal,  363,  397. 

—  of  Vicq  d'Azyr,  414. 
Trai^ezium,  391. 
Trophospongium,  4,  143. 
Tympanum,  469. 

Uretkr,  328. 
Urethra,  231. 
Urinary  bladder,  329. 
Uriniferous  tubules,  course  of,  322. 
Uterus,  352. 
Utricle,  473. 

Vas  deferens,  335. 
Vasa  vasorum,  196. 
Vasoformative  cells,  36,  196. 
Veins,  structure  of,  189. 

—  valves  of,  190. 

—  variations  in,  190. 
Vermiform  appendix,  308. 
Vesiculaj  seminales,  336. 
Villi,  arachnoidal,  442. 

—  of  intestine,  302. 

—  of  synovial  membrane,  91. 
Vitreous  humoiir,  466. 
Volkmann,  canals  of,  99. 

Wallerian  degeneration,  154,  360. 
Warming  apparatus,  48. 
Weigert-Pal  method  for  staining  sec- 
tions of  the  nervous  system,  496. 
Woollen  fibres,  27. 

Yeast,  27. 


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